#include <stdio.h>

int main ( )
{
    int n;
    scanf("%d",&n);
    int i=1,sum=0;
    for (i=1;i<=n;i++){
        int jc=1;
        while(i!=0){
            jc=jc*i;
            i--;
        sum+=jc;
        }
    }
    printf("%d",sum);
    
    return 0;
}