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

constexpr int maxn = 2000000 + 10;

ifstream f("ciur.in");
ofstream g("ciur.out");
int n;
bitset<maxn> isnt_prime = 0;

int main(){
    f >> n;
    isnt_prime[1] = 1;
    for(int i = 2; i * i <= n; ++i)
        if(!isnt_prime[i])
            for(int j = i * i; j <= n; j += i)
                isnt_prime[j] = 1;
    g << n - isnt_prime.count();
    return 0;
}