出大问题！！求大佬回答！！

#include <bits/stdc++.h>
using namespace std;
map<char, char> a, b, c, d;
int main()
{
    int n;
    char x, y;
    cin >> n;
    for (int i = 1; i <= n; i++)
    {
    	cin >> x >> y;
    	if (x == 'D')
			a[y] = 1;
		else if (x == 'C')
			b[y] = 1;
		else if (x == 'H')
			c[y] = 1;
		else
			d[y] = 1;	
	}
	cout << (13 - a.size()) + (13 - b.size()) + (13 - c.size()) + (13 - d.size());
    return 0;
}