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

int main ( )
{
  float area_person;
  float earth_area;
  float earth_area_dry;
  float earth_pop;
  float pi;
  float r;
  float side_person;
//
//  R is radius in km.
//
  r = 6371;
  pi = 3.14159265;
  earth_area = 4 * pi * r * r;
  earth_area_dry = 0.30 * earth_area;
  earth_pop = 6800000000;
  area_person = earth_area_dry / earth_pop;
  side_person = sqrt ( area_person );
//
//  Convert from km to feet.
//
  side_person = side_person * 3280.8399;
  printf ( "Each person gets a plot that is %g feet on a side\n", side_person );
  return 1;
}