#include <bits/stdc++.h>

using namespace std;

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

int v[2000005];

int main() {
    int i,j,N, sol = 0;
    fin>>N;
    for(i = 2; i <= N; i++){
        if(v[i] == 0){
            sol++;
            for(j = 2*i; j <= N; j+=i){
                v[j] = 1;
            }
        }
    }
    fout<<sol;
    return 0;
}