#include <bits/stdc++.h>
using namespace std;
	
bool ciur[2000000];
int main(void){
    ofstream cout("ciur.out");
    ifstream cin("ciur.in");
    int n;
    cin >> n;
    int cnt = 0;
    for(int i = 2;i<=n;i++){
        if(!ciur[i]){
            ++cnt;
            for(int j = 2;j*i<=n;j++){
                ciur[i*j] = true;
            }
        }
    }
    cout << cnt;
}