#include<fstream>
#include<vector>
#include<cmath>
using namespace std;

int n;
vector<bool> PRIM;

int main() {
    ifstream fin("ciur.in");
    ofstream fout("ciur.out");

    fin>>n;
    PRIM.resize(n, true);
    int count = 0;

    for(int i=2; i<=n; i++) {
        if(PRIM[i]) {
            for(int j=2*i; j<=n; j+=i) {
                PRIM[j] = false;
            }
            count++;
        }
    }

    fout<<count;
}