#include <bits/stdc++.h>

using namespace std;

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

const int DIM = 2000000 + 5;

bool f[DIM];

int Ciur(int n)
{
    int ans = 0;
    for(int i = 2; i <= n; ++i) {
        if(f[i] == false) {
            ++ans;
            for(int j = i + i; j <= n; j += i) f[j] = true;
        }
    }
    return ans;
}

int main()
{
    int n;

    fin >> n;
    fout << Ciur(n);
    return 0;
}