#include <fstream>

using namespace std;

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

#define NMAX 2000000

bool ciur[NMAX + 1];

int main() {
    int n, i, d, cnt;
    cin >> n;
    cnt = 0;
    for ( i = 2; i <= n; i++ ) {
        if ( ciur[i] == 0 ) {
            cnt++;
            for ( d = i * i; d <= n; d += i ) {
                ciur[d] = 1;
            }
        }
    }
    cout << cnt;
    return 0;
}