/* 
   avg2.c: find avg in counting sample output data
*/


#include <stdio.h>
#include <stdlib.h>
#include <math.h>

int main(int argc, char ** argv)
{
   int N;
   double p, x, cum;
   int  c1, c2, count;
  
   N = 0;
   cum = 0;

   scanf("%lf\n", &p);

   if ( p >= 1 )
   {
      printf("Warning: first value in input = %lf (a value < 1 was expected)\n",
	 p);
      printf("You have probably used INCORRECT input data\n");
      printf("This program computes the avg for the OUTPUT data files\n");
      printf("Use avg to compute the avg for the INPUT file !\n");
      exit(1);
   }

   while ( scanf("%lf%d\n", &x, &count) > 0 )
   {
      c1 = (int) count - 1;
      c2 = (int) 1/p;

      cum += (c1 + c2) * x;     // Cummulative
      N += (c1 + c2);		// Count
/*
      printf("%d  count=%d\n", j, count[j]);
*/
   }

   printf("N=%d  cum=%lf\n", N, cum);

   printf("Avg = %lf\n", cum/N);
}