#include <fstream>
#include <vector>

using namespace std;

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

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