C++ :

#include <cstdio>
/* 无向图并查集统计连通块个数（自环不影响）。N,M<=20000。 */
static int fa[20005];
int find(int x){ while(fa[x] != x){ fa[x] = fa[fa[x]]; x = fa[x]; } return x; }
int main(){
    int n, m;
    if(scanf("%d %d", &n, &m) != 2) return 0;
    for(int i = 1; i <= n; i++) fa[i] = i;
    int comp = n;
    for(int i = 0; i < m; i++){
        int x, y;
        if(scanf("%d %d", &x, &y) != 2) break;
        int a = find(x), b = find(y);
        if(a != b){ fa[a] = b; comp--; }
    }
    printf("%d\n", comp);
    return 0;
}