library SafeMathInt {

    /**
    * @dev Subtracts two numbers
    */
    function sub(int a, int b) internal pure returns (int) {
        int c = a - b;
        require(c <= a, "sub failed");
        return c;
    }

    /**
    * @dev Adds two numbers
    */
    function add(int a, int b) internal pure returns (int) {
        int c = a + b;
        require(c >= a, "add failed");
        return c;
    }
}
function sub(int a, int b) internal pure returns (int) {
    int c = a - b;
    require(c <= a, "sub failed");
    return c;
}

/**
 * @dev Subtracts two numbers
 */