#include <vector>
#include <iostream>
#include <utility>
using namespace std;

#define DMAX 2000002

int n;
bool ciur[DMAX];

int main(){
	int i, j;

	freopen("ciur.in", "r", stdin);
	freopen("ciur.out", "w", stdout);

	cin >> n;

	for (i = 2; i < DMAX; i++){
		if (!ciur[i]){
			for (j = i*i; j < DMAX; j+=i){
				ciur[j] = true;
			}
		}
	}

	for (i = 2, j = 0; i < n; i++){
		if (!ciur[i])
			j++;
	}
	
	cout << j;

	return 0;
}