#include <fstream>

using namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");
bool c[2000001];

void Ciur()
{
    c[2] = 1;
    for(int i = 3; i <= 2000000; i += 2)
        c[i] = 1;

    for(int i = 3; i * i <= 2000000; i += 2)
        if(c[i] == 1)
            for(int j = i * i; j <= 2000000; j += 2 * i)
                c[j] = 0;
}

int main()
{
    int n, nr_prime = 0;
    fin >> n;
    Ciur();
    nr_prime = 1;
    for(int i = 3; i <= n; i = i + 2)
        if(c[i] == 1)
            nr_prime++;

    fout << nr_prime;

    return 0;
}