// 3-point moving average
//
#include <stdio.h>
#include <math.h>

int main( void)
{
  double d, y1 = 0, y2 = 0, y3 = 0;

  while( scanf("%lf",&d) == 1) { // until end-of-file or error

    y1 = y2; y2 = y3; y3 = d; // slide window

    printf("%g\n", (y1+y2+y3)/3 ); // print average
    
  }
  return 0;
}