#include <iostream>
#include <fstream>
using namespace std;

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

int n, nr = 0;
char c[2000001];

int main() {
    cin>>n;
    for(int i = 2; i*i <= n; i++) {
        if(c[i] == 0) {
            for(int j = 2; j <= n/i; j++)
                c[i*j] = 1;
        }
    }
    for(int i = 2; i <= n; i++)
        if(c[i] == 0)
            nr++;
    cout<<nr;
    return 0;
}