#include <iostream>
#include <fstream>

using namespace std;

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

int ciur[2000000] = {0};

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