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

bool ciur[2000005];
int n, nr, i, j;
int main() {
    in >> n;
    for(i = 2; i <= n; i++)
        if(!ciur[i]) {
            nr++;
            for(j = i*i; j <= n; j += i)
                ciur[j] = 1;
        }
    out << nr;

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