50分求助

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