function getCurrentRate() public view returns (uint256) {
        if (block.timestamp < 1528156799) {         
            return 1050;
        } else if (block.timestamp < 1528718400) {  
            return 940;
        } else if (block.timestamp < 1529323200) {  
            return 865;
        } else if (block.timestamp < 1529928000) {  
            return 790;
        } else {
            return 750;
        }
    }