#include <iostream>
using namespace std;

string mingleStrings(string s1, string s2, int index) {
    if (index >= s1.length()) {
        return "";
    } else {
        string mingled = "";
        mingled += s1[index];
        mingled += s2[index];
        mingled += mingleStrings(s1,s2,++index);
        return mingled;
 }

}

int main() {
	cout << mingleStrings("cat", "dog", 0) << endl;
	return 0;
}