#include <bits/stdc++.h>
#define DIM 3000001

using namespace std;

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

bitset <DIM> prime;

int n;

int solve(int n){
    int answer = 0;
    for(int i=2;i<=n;i++)
        if(!prime[i]){
            answer++;
            for(int j=2;j*i<=n;j++)
                prime[i * j] = 1;
        }
    return answer;
}

int main(){

    ios :: sync_with_stdio(false);
    fin.tie(0);
    fout.tie(0);

    fin >> n;

    fout << solve(n);

    fin.close();
    fout.close();
    return 0;
}