#include<bits/stdc++.h>
#define in f
#define out g
#define MAXN 2000001
using namespace std;

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

bool prime[MAXN];
int n, counter;

int main() {
    in >> n;

    for(int i = 1; i <= n; i++)
        prime[i] = true;

    for(int i = 3; i <= n; i += 2) {
        if(prime[i] == true) {
            counter++;

            for(int j = i + i; j <= n; j += i) {
                prime[i] = false;
            }
        }
    }

    out << counter;
    return 0;
}