#include <fstream>
#include <bitset>
using namespace std;
ifstream in("ciur.in");
ofstream out("ciur.out");

bitset < 2000005 > ciur;

int n, nr;
int main() {
    in >> n;
    ciur[0] = ciur[1] = 1;
    for(int i = 2; i <= n; i++)
        if(!ciur[i]) {
            nr++;
            for(int j = i*i; j <= n; j += i)
                ciur[j] = 1;
        }
    out << nr;

    in.close();
    out.close();
    return 0;
}