#include<stdio.h>
int main()
{
int n;
unsigned long long factorial = 1;
if (scanf("%d",&n) != 1;{
    printf("Invalid Input\n");
    return 1;
}

if(n<0)
{
printf("Invalid Input\n");
}else{
    for(int i = 1;i <= n;i++){
        factorial *= i;
    }
    printf("%llu\n", factorial);
}
return 0;
}