# include <stdio.h>
int main()
{
    _int64 n,m,s,t;
    s=1;
    m=1;
    t=2;
    scanf("%I64d",&n);
    while(t<=n)
    {
        m=m*t;
        s=s+m;
        t=t+1;
    }
    printf("%I64d\n",s);
    return 0;
}此程序在VC上验证多次答案正确，可提交作业却还是个错误