func: function presaleUnfreeze(uint step) external{
          
          assert(unfroze[step][msg.sender] == false);
          assert(DRC.freezeOf(msg.sender) > 0 );
          assert(unfreezeStartTime > 0);
          assert(msg.sender != platform);
          
          uint256 freeze  = DRC.freezeOf(msg.sender);
          uint256 unfreezeAmount = 0;
  
          if(step == 1){
              require( block.timestamp > (unfreezeStartTime + 30 days));
              unfreezeAmount = freeze / 3;
          }
          else if(step == 2){
              require( block.timestamp > (unfreezeStartTime + 60 days));
              unfreezeAmount = freeze / 2;
          }
          else if(step == 3){
              require( block.timestamp > (unfreezeStartTime + 90 days));
              unfreezeAmount = freeze;
          }
          else{
              throw ;
          }
          
          require(unfreezeAmount > 0 );
          
          DRC.unfreeze(msg.sender,unfreezeAmount);
          unfroze[step][msg.sender] = true;
      }