#include <stdio.h>

int fact(int N);

int main(void) {
    int N;
    printf("Input number\n");
    scanf("%d", &N);
    if (N < 0) {
        printf("Factorial not defined for negative numbers\n");
        return -1;
    }
    printf("%d\n", fact(N));
    return 0;
}

int fact(int N) {
    if (N <= 1)
        return 1;
    else
        return N * fact(N - 1);
}