#include <bits/stdc++.h>

using namespace std;
ifstream f("ciur.in");
ofstream g("ciur.out");

const int NMax = 2000005;

int n,NR;
bool p[NMax];

int main()
{
    f >> n;
    for(int i = 3; i < n; i += 2){
        if(p[i] == 0){
            NR++;
            for(int j = i + i; j < n; j += i){
                p[j] = 1;
            }
        }
    }
    if(n >= 2)
        NR++;
    g << NR << '\n';
    return 0;
}