POJ 2524 Ubiquitous Religions

#include<cstdio>
#include<iostream>
#include<set>
using namespace std;
#define N 55000
int F
;
int find(int x)
{
if(F[x] != x)
F[x] = find(F[x]);
return F[x];
}
int main ()
{
int n, m;
int t = 1;
while(scanf("%d %d", &n, &m) != EOF)
{
if(n == 0 && m == 0) break;
for(int i = 1; i <= n; i++)
F[i] = i;

for(int i = 1; i <= m; i++)
{
int a, b;
scanf("%d %d", &a, &b);

int fa = find(a);
int fb = find(b);
if(fa != fb)
F[fb] = fa;
}
set<int>ans;
for(int i = 1; i<= n;i++)
ans.insert(find(F[i]));
printf("Case %d: %d\n",t++, ans.size());

}
return 0;
}