#include <bits/stdc++.h>

using namespace std;

const int maxn = 2e6 + 5;

int a[maxn];

int main()  {
    ifstream cin("ciur.in");
    ofstream cout("ciur.out");
    int n;
    cin >> n;
    int nr = 0;
    for(int i = 2;i <= n;i++)  {
        if(a[i] == 0)  {
            nr++;
            for(long long j = 1LL * i * i;j <= n;j += 1LL * i)  {
                a[j] = 1;
            }
        }
    }
    cout << nr;
    return 0;
}