function keys(uint256 _eth) 
        internal
        pure
        returns(uint256)
    {
        return ((((((_eth).mul(1000000000000000000)).mul(312500000000000000000000000)).add(5624988281256103515625000000000000000000000000000000000000000000)).sqrt()).sub(74999921875000000000000000000000)) / (156250000);
    }