#include <fstream>
#include <iostream>
#define nmax 2000000

using namespace std;

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

int n, c[nmax];

int main(){

    int sol = 0;
    fin >> n;
    for(int i = 2; i <= n; ++i)
        if(c[i] == 0){
            sol++;
            for(int j = i + i; j <= n; j += i)
                c[j] = 1;
        }
    fout << sol;
    return 0;
}