#include<stdio.h>
int main()
{
int n,i;
scanf("%d",&n);
int sum=0,result=1;//易错点:result初始化为0
for (i=1;i<=n;i++) {
result*=i;
sum+=result;
}
printf("%d",sum);
return 0;
}

#include<stdio.h>
int main()
{
int n,i;
scanf("%d",&n);
int sum=0,result=1;//易错点:result初始化为0
for (i=1;i<=n;i++) {
result*=i;
sum+=result;
}
printf("%d",sum);
return 0;
}