#include <bits/stdc++.h>

using namespace std;
ifstream fin ("ciur.in");
ofstream fout ("ciur.out");
long long n,a,b,i,j,nr;

const int N = 2e6+5;

bitset <N> primes;

int main()
{
    fin>>n;
    primes.set();
    for (i=2; i<=n; i++)
    {
        if (primes[i]==1)
        {
            nr++;
            for (j=i;j<=n;j+=i)
                primes[i+j]=0;
        }

    }
    fout<<nr;
    return 0;
}