#include <bits/stdc++.h>

using namespace std;

const int LIM = 10000000;
bool esPrimo[LIM+1];

vector <int> criba()
{
    esPrimo[2] = true;
    for(int i=3; i<=LIM; i+=2)
        esPrimo[i] = true;

    for(int i=3; i*i <= LIM; i++)
        if(esPrimo[i])
            for(int j=i*2; j<=LIM; j+=i)
                esPrimo[j] = false;

    vector <int> primos;
    for(int i=2; i<=LIM; i++)
        if(esPrimo[i])
            primos.push_back(i);

    return primos;
}

int main()
{
    auto p = criba();

    cout << p.size() << endl;


    return 0;
}