#include <fstream>
#include <vector>

using namespace std;

int main() {
    ifstream fin("ciur.in");
    ofstream fout("ciur.out");

    int n, count = 1;
    vector<bool> nprimes;
    fin>>n;
    nprimes.resize(n+1);
    for(int i=3;i<=n;i+=2)
        if(!nprimes[i]){
            count++;
            for(int d=2*i;d<=n;d+=i)
                nprimes[d] = true;
        }
    fout<<count;
    return 0;
}