#include <bits/stdc++.h>

using namespace std;

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

const int Nmax=5000001;
bitset<Nmax>ciur;

int main()
{
    int n, nr = 1;
    ciur[0] = 1;
    
    fin >> n;
    
    for (int i=1; ((i * i) << 1) + (i << 1) <= n; i++)
    {
        if (!ciur[i])
        {
            for (int j = ((i * i) << 1) + (i << 1); (j << 1) + 1 <= n; j += (i<<1)+1)
                ciur[j] = 1;
        }
    }
    
    for (int i=1; 2 * i + 1 <= n; ++i)
        if (ciur[i] == 0) nr++;
    
    fout << nr;
    
    return 0;
}