#include <fstream>

#define Nmax 2000100

using namespace std;

int N, Solution;
bool used[Nmax];

void Sieve() {

    int i, j;

    Solution = 1;

    for(int i = 3; i <= N; i += 2)
        if(!used[i]) {

            ++Solution;

            if(i < 2000)
                for(j = i * i; j <= N; j += (i << 1))
                    used[j] = true;

        }

}
void Read() {

    ifstream in("ciur.in");
    in >> N;
    in.close();

}
void Write() {

    ofstream out("ciur.out");
    out << Solution << '\n';
    out.close();

}
int main() {

    Read();
    Sieve();
    Write();

    return 0;

}