#include <fstream>
#include <bitset>
#include <vector>
#define pb push_back
#define int long long
using namespace std;
using pii = pair<int,int>;
bitset <2000001> sieve;
int n, sz;
vector <int> primes;
ifstream cin("ciur.in");
ofstream cout("ciur.out");
signed main(){
    cin >> n;
    for(int i = 2 ; i <= n ; i++)
    {
        if(sieve[i]==0)
        {
            primes.pb(i);
            sz++;
        }
        for(int j = 0 ; j < sz && primes[j]*i <= n; j++)
        {
            sieve[primes[j]*i] = 1;
            if(i%primes[j]==0) break;
        }
    }
    cout << sz ;
    return 0;
}