#include <iostream>
#include <fstream>
using namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");

int n, numere=0;
bool prim[2000005];

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

}