/*   loop01.c               */

#include <stdio.h>

int main(void)
{
    int i,n,s;

    s=0;
    printf("n=");
    scanf("%d",&n);

    if ((n>0) && (n<=20))
    {
         for (i=1; i<=n; i++) {
              printf("i=%d\n",i);
              s=s+i;
         }
         printf("sum=%d\n",s);
     }
     else
     {
         printf("1 <= n <= 20\n");
     }

  return 0;
}