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