#include<bits/stdc++.h>
#include"testlib.h"
using namespace std;
using ll = long long;

const ll Nmin = 1, Nmax = 200'000;

int main(){
    registerValidation();
    ll n = inf.readLong(Nmin,Nmax);
    inf.readEoln();
    string s = inf.readString();
    string t = inf.readString();
    inf.readEof();
    inf.ensuref((int)(s.size()) == n, "size of s must be N");
    inf.ensuref((int)(t.size()) == n, "size of t must be N");
    for (auto c : s){
        inf.ensuref(c == 'A' || c == 'B' || c == 'C', "S must be consist of only A or B or C");
    }
    for (auto c : t){
        inf.ensuref(c == 'A' || c == 'B' || c == 'C', "T must be consist of only A or B or C");
    }
}