#include <fstream>
using namespace std;
int main()
{
        ifstream fin("ciur.in");
    ofstream fout("ciur.out");

    int i, j;
    int N, cnt=0;
    char prim[2000005];
    fin >> N;
    for (i = 2; i <= N; ++i)
        prim[i] = 1;
    for (i = 2; i <= N; ++i)
        if (prim[i])
        {
            ++cnt;
            for (j = i+i; j <= N; j += i)
                prim[j] = 0;
        }

    fout << cnt << "\n";

    return 0;
}