#include <fstream>
#define nmax 1000000
using namespace std;

ifstream cin("ciur.in");
ofstream cout("ciur.out");

int v[nmax];

void ciur(int n){
    v[0] = 1, v[1] = 1;
    for(int i = 2; i * i <= nmax; ++i){
        if(v[i] == 0){
            for(int j = 2; i * j <= nmax; ++j){
                v[i * j] = 1;
            }
        }
    }
}

int main(){
    int n, cnt = 0;
    cin >> n;
    ciur(nmax);
    for(int i = 1; i <= n; ++i){
        if(v[i] == 0){
            cnt++;
        }
    }
    cout << cnt;
    return 0;
}