#include <fstream>

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

bool v[2000001];
int main()
{
    long long N, c=1, i, j;
    in>>N;
    for(i=3; i<=N; i+=2)
    {
        if(v[i]==0)
        {
            for(j=i*2; j<=N; j+=i)
            {
                v[j]=1;
            }
            c++;
        }
    }
    out<<c;



    return 0;
}