#include <fstream>

using namespace std;
ifstream cin("ciur.in");
ofstream cout("ciur.out");

short int ciur[2000001];

int main()
{
    int n, nrprime = 0;
    cin>>n;
    for(int i = 2; i <= n; ++i)
    {
        if(ciur[i] == 0)
        {
            ++nrprime;
            for(int j = i * 2; j <= n; j += i )
            {
                ciur[j] = 1;
            }
        }
    }
    cout<<nrprime;
    return 0;
}