Counting Canals

input/code.cpp: In function 'int main()':
input/code.cpp:21:17: error: no 'operator++(int)' declared for postfix '++' [-fpermissive]
  string rr = aa ++ bb;
              ~~~^~

#include <iostream>
#include <string>
using namespace std;

int main () {
	int a;
	int b;
	int f;
	cin >> a;
	cin >> b;
	cin >> f;
	string aa;
	string bb;
	string ff;
	cin >> aa;
	cin >> bb;
	cin >> ff;
	if (f < b || f < a){
		exit(0);
	}
	string rr = aa ++ bb;
	if (rr.find(ff) == string::npos){
		cout << "YES";
		exit(0);
	}
	rr = bb + aa;
	if (rr.find(ff) == string::npos){
		cout << "YES";
		exit(0);
	}
	cout << "No";

}