contract SafeMath {
    //internals

    function safeMul(uint a, uint b) internal pure returns(uint) {
        uint c = a * b;
        assert(a == 0 || c / a == b);
        return c;
    }

    function safeSub(uint a, uint b) internal pure returns(uint) {
        assert(b <= a);
        return a - b;
    }

    function safeAdd(uint a, uint b) internal pure returns(uint) {
        uint c = a + b;
        assert(c >=a && c >= b);
        return c;
    }
}
function safeMul(uint a, uint b) internal pure returns(uint) {
        uint c = a * b;
        assert(a == 0 || c / a == b);
        return c;
    }
//internals