#include <iostream>

using namespace std;

int main(void)
{
  float p = 1;
  for (int i = 0; i < 40; i++)
      p *= (float) (365 - i) / (float) 365;
  
  cout << "Probability at least two people have the same birthday is " <<
  1 - p << endl;


  return 0;
}

Probability at least two people have the same birthday is 0.891232