#include <bits/stdc++.h>

using namespace std;

const int NMAX = 1e6;
bitset <NMAX + 5> f;

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