function get_exchange_wei() returns(uint256){

        
		uint len = exchangeRateArray.length;  
		uint nowTime = block.timestamp;
        for(uint i = 0; i < len; i += 3){
            
			exchangeRate memory rate = exchangeRateArray[i];
            uint time1 = rate.time1;
            uint time2 = rate.time2;
            uint value = rate.value;
			if (nowTime>= time1 && nowTime<=time2) {
				tokenExchangeRateInWei = value;
				return value;
			}
            
        }
		return tokenExchangeRateInWei;
	}