#include <fstream>

using namespace std;

ifstream fin("ciur.in");
ofstream fout("ciur.out");

int n;
bool v[2000005];

void ciur()
{
    for(int i = 4; i <= n; i += 2)
    {
        v[i] = 1;
    }
    for(int i = 3; i * i <= n; i += 2)
        if(v[i] == 0)
    {
        for(int j = i * i; j <= n; j += 2 * i)
            v[j] = 1;
    }
    int k = 0;
    for(int i = 2; i <= n; i ++)
    {
        if(v[i] == 0)
        {
            k ++;
        }
    }
    fout << k;
}

int main()
{
    fin >> n;
    ciur();
    return 0;

}