#include <stdio.h>

int main() {
    long long int n, s = 0;
    long long int f[100];
    scanf("%lld", &n);
    int fac = 1;
    for (int i = 1; i <= n; i++) {
        f[i] = fac *= i;
    }
    for (int j = 1; j <= n; j++) {
        s += f[j];
    }
    printf("%lld", s);
    return 0;
}