#include <iostream>
#include <fstream>

using namespace std;

char prime[2000002];

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

    int i, j, n, cnt = 0;
    fin >> n;

    for (i = 2; i <= n; i+=2){
        prime[i] = 1;
    }
    cnt++;
    for (i = 3; i <= n; i++){
        if (prime[i] == 0){
            cnt++;
            for (j = i*i; j <= n; j+=i){
                prime[j] = 1;
            }
        }
    }
    fout << cnt;
    return 0;
}