you give stre s robot currently hold string t apply follow operation s t emptyremove character string s robot the robot append character string tRemove character string t robot the robot write character paperreturn lexicographically small string write paper Example 1input s zzaoutput azzexplanation let p denote write stringinitially p szza tPerform operation time p s tzzaperform second operation time pazz s tExample 2input s bacoutput abcexplanation let p denote write stringperform operation twice p sc tba Perform second operation twice pab sc t perform operation pab s tc perform second operation pabc s tExample 3input s bddaOutput addbexplanation let p denote write stringinitially p sbdda tperform operation time p s tbddaperform second operation time paddb s t Constraints1 slength 105s consist english lowercase letter