#include <fstream>
#define N 2000001
using namespace std;

ifstream in("ciur.in");
ofstream out("ciur.out");

int n, nr;
bool ciur[N];


int main()
{
    in>>n;

    for(int i = 2; i <= n; ++i)
        if(!ciur[i]){
            nr++;
            for(int j = i + i; j <= n ; j += i)
                ciur[j] = 1;
        }
    out<<nr;

    in.close();
    out.close();
    return 0;
}