``pragma solidity ^0.5.0;contract ERC20 {    // Safemath    function add(uint256 a, uint256 b) internal pure returns (uint256) {        uint256 c = a + b;        require(c >= a, "SafeMath: addition overflow");        return c;    }    function sub(uint256 a, uint256 b) internal pure returns (uint256) {        require(b <= a, "SafeMath: subtraction overflow");        uint256 c = a - b;        return c;    }    function mul(uint256 a, uint256 b) internal pure returns (uint256) {        // Gas optimization: this is cheaper than requiring 'a' not being zero, but the        // benefit is lost if 'b' is also tested.        // See: https://github.com/OpenZeppelin/openzeppelin-contracts/pull/522        if (a == 0) {            return uint256(0);        }        uint256 c = a * b;        require(c / a == b, "SafeMath: multiplication overflow");        return c;    }    function div(uint256 a, uint256 b) internal pure returns (uint256) {        require(b > 0, "SafeMath: division by zero");        uint256 c = a / b;        return c;    }    function mod(uint256 a, uint256 b) internal pure returns (uint256) {        require(b != 0, "SafeMath: modulo by zero");        return a % b;    }    // // real contract    mapping (address => uint256) private _balances;    mapping (address => mapping (address => uint256)) private _allowances;    uint256 private _totalSupply;    function totalSupply() public view returns (uint256) {        return _totalSupply;    }    function balanceOf(address account) public view returns (uint256) {        return _balances[account];    }    function _transfer(address _sender, address recipient, uint256 amount) internal {        require(_sender != address(0), "ERC20: transfer from the zero address");        require(recipient != address(0), "ERC20: transfer to the zero address");        _balances[_sender] = sub(_balances[_sender], amount);        _balances[recipient] = add(_balances[recipient], amount);    }    function transfer(address recipient, uint256 amount) public returns (bool) {        _transfer(msg.sender, recipient, amount);        return true;    }    function allowance(address owner, address spender) public view returns (uint256) {        return _allowances[owner][spender];    }    function _approve(address owner, address spender, uint256 value) internal {        require(owner != address(0), "ERC20: approve from the zero address");        require(spender != address(0), "ERC20: approve to the zero address");        _allowances[owner][spender] = value;    }    function approve(address spender, uint256 value) public returns (bool) {        _approve(msg.sender, spender, value);        return true;    }    function transferFrom(address _sender, address recipient, uint256 amount) public returns (bool) {        _transfer(_sender, recipient, amount);        _approve(_sender, msg.sender, sub(_allowances[_sender][msg.sender], amount));        return true;    }    function increaseAllowance(address spender, uint256 addedValue) public returns (bool) {        _approve(msg.sender, spender, add(_allowances[msg.sender][spender], addedValue));        return true;    }    function decreaseAllowance(address spender, uint256 subtractedValue) public returns (bool) {        _approve(msg.sender, spender, sub(_allowances[msg.sender][spender], subtractedValue));        return true;    }    function _mint(address account, uint256 amount) internal {        require(account != address(0), "ERC20: mint to the zero address");        _totalSupply = add(_totalSupply, amount);        _balances[account] = add(_balances[account], amount);    }    function _burn(address account, uint256 value) internal {        require(account != address(0), "ERC20: burn from the zero address");        _balances[account] = sub(_balances[account], value);        _totalSupply = sub(_totalSupply, value);    }    function _burnFrom(address account, uint256 amount) internal {        _burn(account, amount);        _approve(account, msg.sender, sub(_allowances[account][msg.sender], amount));    }}``