#include <fstream>
#include <bitset>

using namespace std;

bitset<2000001> b;
int n, i, j, nr;

int main() {
    ifstream fin("ciur.in");
    ofstream fout("ciur.out");
    fin>>n;
    for (i=2;i<=n;i++)
        if (b[i] == 0) {
            nr++;
            for (j=i+i;j<=n;j+=i)
                b[j] = 1;
        }
    fout<<nr<<"\n";

    return 0;
}