#include <cstdio>
#include <map>

std :: map<int, int> a;
int ans = 0, n, c;

int main() {
        while (scanf("%d", &n) == 1)
                for (; n; n--)
                        scanf("%d", &c), ans += ++a[c] == 3;
        printf("%d", ans);
}

Edited by author 05.11.2011 20:31

can you explain the function/name "map" ?
which language used in code above?

map is in C++ STL and it is like a binary search tree.

amazing solve!!