#include <iostream>
#include <cstring>
using namespace std;

bool arr[100000005];

int main()
{
    int n, ans = 0;
    cin >> n;
    arr[1] = true;
    for(int i = 2; i <= n; i++)
    {
        if(!arr[i])
        {
            ans++;
            for(int j = i + i; j <= n; j += i)
            {
                arr[j] = true;
            }
        }
    }
    cout << ans << endl;
    return 0;
}