pragma solidity ^0.4.11; 



contract Zerk {
    
    uint public constant _totalSupply = 20000000;
    
    string public constant symbol ="ZRK";
    string public constant name ="Zerk";
    uint8 public constant decimals =0;
    
        
    mapping(address => uint256) balances;
    mapping(address => mapping(address => uint256)) allowed;
    
    
        
        
    function Zerk() {
        balances[msg.sender] = _totalSupply;
    }
    function totalSupply() constant returns (uint256 totalSupply) {
        return _totalSupply;
    }
    
    function balanceOf(address _owner) constant returns (uint256 balance) {
        return balances[_owner];
        
        
    }
    
    function transfer(address _to, uint256 _value) returns (bool success) {
        require(
            balances[msg.sender] >= _value
            && _value > 0);
        balances[msg.sender] -= _value;
        balances[_to] += _value;
        Transfer(msg.sender, _to,  _value);
        return true;
        
        }

    function transferFrom(address _from, address _to, uint256 _value) returns (bool success) {
        require (
             allowed[_from][msg.sender] >= _value
             && balances [_from] >= _value
             && _value >0
             );
             balances[_from] -= _value;
             balances[_to] += _value;
             allowed[_from][msg.sender] -= _value;
             Transfer(_from, _to, _value);
             return true;
             
    }
    function approve(address _spender, uint256 _value) returns (bool success) {
        allowed[msg.sender][_spender] = _value;
        Approval(msg.sender, _spender, _value);
        return true;
    }
    function allowance(address _owner, address _spender) constant returns (uint256 remaining)
{
    return allowed[_owner][_spender];
    
}    
    event Transfer(address indexed _from, address indexed _to, uint256 _value);
    event Approval(address indexed _owner, address indexed _spender, uint256 _value);
    
}

interface IERC20 {
    function totalSupply() constant returns (uint256 totalSupply);
    function balanceOf(address _owner) constant returns (uint256 balance);
    function transfer(address _to, uint256 _value) returns (bool success);
    function transferFrom(address _from, address _to, uint256 _value) returns (bool success);
    function approve(address _spender, uint256 _value) returns (bool success);
    function allowance(address _owner, address _spender) constant returns (uint256 remaining);
    event Approval(address indexed _owner, address indexed _spender, uint256 _value);
}