#include <iostream>
#include <cstdio>

using namespace std;

int ans, N, CE[2000005];

void Ciur() {
    CE[0] = CE[1] = 1;

    for(int i = 2; i <= N; ++i) {
        if(CE[i] == 0) {
            ++ans;

            for(int j = i * i; j <= N; j += i) {
                CE[j] = 1;
            }
        }
    }
}

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

    scanf("%d", &N);

    Ciur();

    cout << ans << '\n';

    return 0;
}