#include <stdio.h>

int fact(n) {
    
    int result = fact(n) + fact(n - 1);
    return result;
}


int main() {
    int n;
    scanf("%d", &n);
    
    if (n < 0) {
        printf("Invalid Input");
        return 0;
    }
    
    printf("%d", fact(n));
    return 0;
}