Problem H: 阶乘和

#include<stdio.h>
int main()
{
    int i=0;
    int ret=1;
    int sum=0;
    int n;
    scanf("%d",&n);
    for(i=1;i<=n;i++)
    {
        ret=ret*i;
        sum+=ret;
    }
    printf("%d\n",sum);
    return 0;
}