#include <cstdio>
int main(){
    long long n, sum = 0, ans = 1;
    scanf("%lld", &n);
    for (int i = 1; i <= n; i++){
        for (int j = i; j >= 1; j--){
            ans *= j;
        }
        sum += ans;
        ans = 1;
    }
    printf("%lld", sum);
    return 0;
}