C++ :

#include <cstdio>
int main(){
    int n, m;
    if(scanf("%d %d", &n, &m) != 2) return 0;
    static int a[1005], gone[1005];
    for(int i = 1; i <= n; i++) scanf("%d", &a[i]);
    for(int i = 0; i < m; i++){ int b; scanf("%d", &b); gone[b] = 1; }
    /* 剩下的球按重量计数，同重量两两配对 -> C(cnt,2) */
    static int cnt[105];
    for(int i = 1; i <= n; i++) if(!gone[i]) cnt[a[i]]++;
    long long ans = 0;
    for(int w = 1; w <= 100; w++) ans += (long long)cnt[w] * (cnt[w] - 1) / 2;
    printf("%lld\n", ans);
    return 0;
}