#include <iostream>
#include <fstream>
#include <bitset>

using namespace std;

ifstream fin("ciur.in");
ofstream fout("ciur.out");
bitset < 2000001 > v;

int main()
{
    int n,nr = 1;
    fin >> n;
    int i = 4;
    while(i <= n){
        v[i] = true;
        i += 2;
    }
    for(int d = 3; d <= n; d += 2){
        if(v[d] == false){
            nr++;
            for(int j = d + d; j <= n; j += d){
                v[j] = true;
            }
        }
    }
    fout << nr;
    return 0;
}