#include<stdio.h>
int main()
{
    int  n,a,b;
    unsigned int c;
    c<=50;
    c>=0;
    long long int S = 0;
    scanf("%d", &c);
    for (n=1; n <= c; n++) {
        b = 1;
        for (a = 1; a <= n ; a++) {
            b = b * a;
        }
        S = S + b;
    }
    printf("%lld", S);
    return 0;
}