#include <bits/stdc++.h>

std::ifstream in("ciur.in");
std::ofstream out("ciur.out");

using namespace std;
const int MAX = 2000002;
bitset < MAX > Prim;
int N;
void CIUR()
{
    Prim[1] = true;
    for ( int i = 2 ; i <= MAX ; ++i)
    {
        if(Prim[i] == 0)
            for ( int j = i+i ; j <= MAX ; j+=i)
            Prim[j] = true;

    }
}
int main()
{
    CIUR();
    int Answer = 0;
    in >> N;
    for ( int i = 1; i <= N ; ++i)
        if(Prim[i] == 0)
        Answer++;
        out << Answer;
}