#include <bits/stdc++.h>
using namespace std;

#define REP(i, s, n) for (int i = s; i < n; ++i)
#define rep(i, n) REP(i, 0, n)
#define SORT(c) sort((c).begin(), (c).end())
#define IINF INT_MAX
#define LLINF LLONG_MAX
#define DEBUG false

int main()
{
    vector<int> prime;
    prime.push_back(2);
    for (long long int i = 3; i < 999999; i++)
    {
        double temp = sqrt(i);
        for (int j = 0;; j++)
        {
            if (temp < prime[j])
            {
                prime.push_back(i);
                break;
            }
            if (i % prime[j] == 0)
            {
                break; //this is not prime
            }
        }
    }
    int n;
    int i;
    while (cin >> n)
    {
        for (i = 0; prime[i] <= n; i++);
        cout << i << endl;
    }
    return 0;
}