#include <cmath>
#include <cstdio>
using namespace std;

double f(double x) {
  if(abs(x) < 1e-15) { return 2.07079632677096370230; }
  constexpr int n = 100000;
  double res = 1 / (2. * (x + n + .5));
  for(int i=0; i<n; ++i) {
    double t = sin(x + i) / (x + i);
    res += t*t;
  }
  return res;
}

int main(void) {
  double x; scanf("%lf", &x);
  double res = f(x);
  printf("%.15lf\n", res);
  return 0;
}