#include <stdio.h>
  #include <stdlib.h>
  #include <string.h>
  #define N 100000000
  int main (int argc, char** argv)
  {
      long long int n;
      long long int i;
  
      double l_sum, x, h;
  
      n=N;
  
      if(argc==2)
      {
          n=atol(argv[1]);
      }
  
  
      h = 1.0/n;
  
      l_sum = 0.0;
      
      for (i = 0; i < n; i ++)
      {
          x = (i + 0.5)*h;
          l_sum += 4.0/(1.0 + x*x);
      }
  
      l_sum *= h;
  
      printf("N=%lld, PI = %0.12g
  ",n ,l_sum);
  
      return 0;
  }