pragma solidity ^0.4.15;

/**
 * @title SafeMath
 * @dev Math operations with safety checks that throw on error
 */
library SafeMath {
  function mul(uint256 a, uint256 b) internal constant returns (uint256) {
    uint256 c = a * b;
    assert(a == 0 || c / a == b);
    return c;
  }

  function div(uint256 a, uint256 b) internal constant returns (uint256) {
    // assert(b > 0); // Solidity automatically throws when dividing by 0
    uint256 c = a / b;
    // assert(a == b * c + a % b); // There is no case in which this doesn't hold
    return c;
  }

  function sub(uint256 a, uint256 b) internal constant returns (uint256) {
    assert(b <= a);
    return a - b;
  }

  function add(uint256 a, uint256 b) internal constant returns (uint256) {
    uint256 c = a + b;
    assert(c >= a);
    return c;
  }
}



using SafeMath for uint;

mapping(address => uint256) balances;

function balanceOf(address _owner) constant returns (uint256 balance) {
  return balances[_owner];
}

function transfer(address _to, uint256 _value) returns (bool) {
   balances[msg.sender] = balances[msg.sender].sub(_value);
   balances[_to] = balances[_to].add(_value);
   Transfer(msg.sender, _to, _value);
   return true;
 }