#include <iostream>
#include <fstream>

using namespace std;

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

const int NMAX = 2000005;
int prim[NMAX];

int main()
{
    int n;
    fin >> n;
    int rasp=0;
    for(int i=2;i<=n;i++)
    {
        if(prim[i]==0)
        {
            rasp++;
            for(long long j=1LL*i*i;j<=n;j+=i)
            {
                prim[j]=1;
            }
        }
    }
    fout << rasp;
    return 0;
}