#include <iostream>
#include <fstream>

using namespace std;

ifstream in("ciur.in"); ///HATZ
ofstream out("ciur.out"); ///JOHNULE

const int NMAX = 2000000;
bool v[NMAX+2];

void sieve(int n)
{
    for(int i=2;i<=n;i++)
    {
        if(v[i]==0)
        {
            for(int j=i*2;j<=n;j+=i)
            {
                v[j]=1;
            }
        }
    }
}

int main()
{
    int n;
    in>>n;
    sieve(n);
    int sol=0;
    for(int i=2;i<=n;i++)
    {
        if(v[i]==0)
            sol++;
    }
    out<<sol;
}