#include <bits/stdc++.h>   using namespace std;   const int inf = 1 << 30;   const int N = 100100;   char a[N], b[N];   int n, m, k, p[27];   int Par(int i) { return p[i] = (i == p[i]) ? i : Par(p[i]); }   bool same(int i, int j) { return Par(i) == Par(j); }   int comp[27];   void mrg(int i, int j) {     if (same(i, j)) return;     i = Par(i);     j = Par(j);     p[i] = p[j];     comp[i] += comp[j];   }   vector<pair<char, char> > v;   int main() {     scanf( %d , &n);     scanf( %s , a);     scanf( %s , b);     for (int i = 0; i < 26; i++) {       p[i] = i;       comp[i] = 1;     }     for (int i = 0; i < n; i++) {       if (same(b[i] -  a , a[i] -  a )) continue;       mrg(b[i] -  a , a[i] -  a );       v.push_back({a[i], b[i]});     }     printf( %d n , v.size());     for (auto x : v) printf( %c %c n , x.first, x.second);     return 0;   }   