#include <stdio.h>                 
#include <stdlib.h> /*for alloc(), free()*/

int main(void) {                
  int i, n, *A, si;

  scanf("%d", &n); 
  A = (int *) malloc(n * sizeof(int)); // allocates n elements

  for (i=0; i<n; i++)  
    A[i] = i;  // alt: *(A+i) = i;      
  si = 0;

  for (i=0; i<n; i++)
    si += A[i];
  printf("sum of 0 to %d = %d\n", n-1, si);

  free(A); // release storage allocated at address A  
           // must not *A after this! 
  return 0;                
}