contract SafeMath { // security reviewed 05/09/17
  function safeMul(uint256 a, uint256 b) internal returns (uint256) {
    uint256 c = a * b;
    safeAssert(a == 0 || c / a == b);
    return c;
  }

  function safeDiv(uint256 a, uint256 b) internal returns (uint256) {
    safeAssert(b > 0);
    uint256 c = a / b;
    safeAssert(a == b * c + a % b);
    return c;
  }

  function safeSub(uint256 a, uint256 b) internal returns (uint256) {
    safeAssert(b <= a);
    return a - b;
  }

  function safeAdd(uint256 a, uint256 b) internal returns (uint256) {
    uint256 c = a + b;
    safeAssert(c>=a && c>=b);
    return c;
  }

  function safeAssert(bool assertion) internal {
    if (!assertion) revert();
  }
}
function safeMul(uint256 a, uint256 b) internal returns (uint256) {
  uint256 c = a * b;
  safeAssert(a == 0 || c / a == b);
  return c;
}

// security reviewed 05/09/17