样例都过了，但是0

#include<iostream>
using namespace std;
#define ll long long
ll n;
char op1,op2;
ll t[128][128];
int main(){
	cin >> n;
	for (int i = 1;i <= n;i++){
		cin >> op1 >> op2;
		ll val,vbl;
		val = op1-'0';
		vbl = op2-'0';
		t[val][vbl]++;
	}
	ll ans = 0;
	for (int i = 1;i <= 128;i++){
		for (int j = 1;j <= 128;j++){
			if (t[i][j] != 0){
				ans++; 
			}
		}
	} 
	cout << 52-ans;
	return 0;
}