pragma solidity ^0.4.24;

library SafeMath {
    function mul(uint256 a, uint256 b) internal pure returns (uint256) {
        if (a == 0) {return 0;}
        uint256 c = a * b;
        assert(c / a == b);
        return c;
    }
    function div(uint256 a, uint256 b) internal pure returns (uint256) {
        uint256 c = a / b;
        return c;
    }

    function sub(uint256 a, uint256 b) internal pure returns (uint256) {
        assert(b <= a);
        return a - b;
    }
    function add(uint256 a, uint256 b) internal pure returns (uint256) {
        uint256 c = a + b;
        assert(c >= a);
        return c;
    }
}
contract ERC20{
    using SafeMath for uint256;
    function balanceOf(address _owner)public view returns (uint256 balance);
    function transfer(address _to, uint256 _value)public returns (bool success);
    function transferFrom(address _from, address _to, uint256 _value)public returns (bool success);
    function approve(address _spender, uint256 _value)public returns (bool success);
    function allowance(address _owner, address _spender)public view returns (uint256 remaining);
    event Transfer(address indexed _from, address indexed _to, uint256 _value);
    event Approval(address indexed _owner, address indexed _spender, uint256 _value);
}
contract VTToken is ERC20{
    string public name   = "Virtual Talk";
    string public symbol = "VT"; 
    uint8 public decimals=18;
    uint256 public totalSupply;
    mapping(address => uint256) balances;
    mapping (address => mapping (address => uint256)) internal allowed;
    
    constructor(uint256 initialSupply)public{
        totalSupply = initialSupply * 10 ** uint256(decimals);
        balances[msg.sender] = totalSupply;
    }
    
    function balanceOf(address _owner)public view returns (uint256 balance){
        return balances[_owner];
    }
    
    function transfer(address _to, uint256 _value)public returns (bool success){
        require(_to != address(0));
        require(_value <= balances[msg.sender]);
        
        balances[msg.sender] = balances[msg.sender].sub(_value);
        balances[_to] = balances[_to].add(_value);
        emit Transfer(msg.sender, _to, _value);
        return true;
    }
     
    function transferFrom(address _from, address _to, uint256 _value)public returns (bool success){
        require(_to != address(0));
        require(_value <= balances[_from]);
        require(_value <= allowed[_from][msg.sender]);
    
        balances[_from] = balances[_from].sub(_value);
        balances[_to] = balances[_to].add(_value);
        allowed[_from][msg.sender] = allowed[_from][msg.sender].sub(_value);
        emit Transfer(_from, _to, _value);
        return true;
    }
    
    function approve(address _spender, uint256 _value)public returns (bool success){
        allowed[msg.sender][_spender] = _value;
        emit Approval(msg.sender, _spender, _value);
        return true; 
    }
    
    function allowance(address _owner, address _spender)public view returns (uint256 remaining){
        return allowed[_owner][_spender];
    }
}