#include <bits/stdc++.h>

using namespace std;

#define forn(i, n) for (int i = 0; i < (int)(n); i++)

const int N = 1e6;

bool p[N];

int E1() {
	int cnt = 0;
	memset(p, 0, sizeof(p));
	for (int i = 2; i < N; i++)
		if (!p[i])
			for (int j = i + i; j < N; j += i)
				p[j] = 1, cnt++;
	return cnt;
}

int E2() {
	int cnt = 0;
	memset(p, 0, sizeof(p));
	for (int i = 2; i * i < N; i++)
		if (!p[i])
			for (int j = i * i; j < N; j += i)
				p[j] = 1, cnt++;
	return cnt;
}

int main() {
	printf("%.4f\n", 1. * E1() / E2());
}
// Output: 1.3078