#include <iostream>
#include <fstream>
#include <math.h>
#define MAX 200004
using namespace std;

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

bool A[MAX];

int SieveOfErathostene(int p) {
    int k = 0;
    for(int i = 1; i <= p; i++)
        A[i] = 1;
    for(int i = 2; i <= sqrt(p); i++)
        if(A[i]) {
            k++;
            for(int j = i * i; j <= p; j = j + i)
                A[j] = 0;
        }
    return k;
}

int main() {
    int n;
    in >> n;
    out << SieveOfErathostene(n);

    return 0;
}