#include <bits/stdc++.h>
using namespace std;
#define MAX 2000005

int ciur[MAX];
int main(void){
    ofstream cout("ciur.out");
    ifstream cin("ciur.in");
    int n;
    cin >> n;
    int cnt = 0;
    for(int i =2;i<=n;i++){
        ciur[i] = 1;
    }
    for (int i = 2; i <= n; ++i)
        if (ciur[i])
        {
            ++cnt;
            for (int j = i+i; j <= n; j += i)
                ciur[j] = 0;
        }
    cout << cnt;
}