#include <fstream>
#include <iostream>

using namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");
int n;
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()
{
 //   cout << sizeof(c) / 1024.0 / 1024.0;
    int ct = 0;
    fin >> n;
    Ciur();
    for(int i = 1; i <= n; i++)
        if(c[i] == 1)
            ct++;
    fout << ct;
    return 0;
}