1!+2!+3!+4!+...n! 0<n<=20

#include<stdio.h>
int main()
{
    unsigned long long i,j,k=1,sum=0;
    int n;
    while(scanf("%d",&n)!=EOF)
    {
        sum=0;
        for(i=1;i<=n;i++)
        {
            k=1;
            for(j=1;j<=i;j++)
            {
                k=k*j;
            }
            sum=sum+k;
        }
        printf("%llu\n",sum);
    }
    return 0;
}