#include <fstream>
#include <vector>
#include <bitset>

using namespace std;

const int maxn = 2000005;

bitset <maxn> used;

int main() {
    ifstream fin("ciur.in");
    ofstream fout("ciur.out");
    int n, ans = 0;
    fin >> n;
    for(int i = 3 ; i <= n ; i += 2) {
        if(used[i])
            continue;
        ++ ans;
        for(int j = i << 1 ; j <= n ; j += i)
            used[j] = 1;
    }
    fout << ++ ans << '\n';
}