#include <iostream>
#include <fstream>

using namespace std;

ifstream fin("ciur.in");
ofstream fout("ciur.out");
int main() {
    char prim[2000005];
    int n, c = 0;
    fin >> n;
    for(int i = 2; i <= n; i++)
        prim[i] = 1;

    for(int i = 2; i <= n; i++) {
        if(prim[i]) {
            c++;
            for(int j = i+i; j <= n; j+=i)
                prim[j] = 0;
        }
    }
    fout << c;

    return 0;
}