#include <bits/stdc++.h>

using namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");
const int dim = 2e6 + 7;
bool viz[dim];
int main()
{
    int n;
    fin >> n;
    int nrprime = 1;
    for(int i = 3; i <= n; i += 2)
    {
        if(viz[i] == 0)
        {
            nrprime++;
            if(1ll * i * i <= n)
            {
                for(int j = i * i; j <= n; j += 2 * i)
                {
                    viz[j] = 1;
                }
            }

        }
    }
    fout << nrprime;
    return 0;
}