#include <iostream>
#include <fstream>
using namespace std;
 
ifstream fin("ciur.in");
ofstream fout("ciur.out");
 
const int MAX_SIZE = 2000000;
char prim[MAX_SIZE + 5];
 
int main() {
    int n;
    int cnt = 0;
    fin >> n;
    for (int i = 2; i <= n; ++i) {
        prim[i] = 1;
    }
    for (int i = 2; i <= n; ++i)
        if (prim[i]) {
            ++cnt;
            for (int j = i + i; j <= n; j += i) {
                prim[j] = 0;
            }
        }
    fout << cnt;
    return 0;
}