Uri 2502 - Deciphering the Encrypted Card

#include<bits/stdc++.h>
using namespace std;

int main()
{
    int n,m;
    string orginal_input,result;
    string s1,s2;
    while(cin >> n >> m){
          multimap < char , int > st1,st2;
          cin.ignore();
          getline(cin,s1);
          getline(cin,s2);
          for(int j = 0 ; j < n ;j++){
            st1.insert(pair < char , int >(s1[j],j));
            st2.insert(pair < char , int >(s2[j],j));
          }
        int index ;
        while(m--){
            getline(cin,orginal_input);
            for(int i = 0;  i < orginal_input.size() ; i++){
                    char ch = toupper(orginal_input[i]);
                if(st1.count(ch) == 0 && st2.count(ch) == 0){
                        result += orginal_input[i];
                }else if(st1.count(ch) != 0){
                    index = st1.find(ch)->second;
                    result += !isupper(orginal_input[i]) ? (char) tolower(s2[index]) : s2[index];
                }else if(st2.count(ch) != 0){
                    index = st2.find(ch)->second;
                    result += !isupper(orginal_input[i]) ? (char) tolower(s1[index]) : s1[index];
                }
            }
            cout << result << endl;
            result.clear();
        }
        cout << endl;
    }

    return 0;
}