#include <bits/stdc++.h>
using namespace std;
const int VMAX = 2e6+2;
bool ciur[VMAX];
int n,cnt;

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

int main()
{
    fin >> n;
    ciur[0] = ciur[1] = 1;
    for(int i = 2; i <= n; i++){
        if(ciur[i] == 0){
            cnt++;
            for(int j = 2*i; j <= n; j += i){
                ciur[j] = 1;
            }
        }
    }
    fout << cnt;
    return 0;
}