#include <fstream>
#define maxn 2000001

using namespace std;
bool A[maxn];

int main()
{
    int n,c=0,i,j;
    ifstream f("ciur.in");
    ofstream g("ciur.out");
    f >> n;
    for (i=2; i<=n; i++)
        A[i] = true;
    for (i=2; i<=n; i++)
        if (A[i] == true)
        {
            c++;
            for (j = i*i; j<=n; j=j+i)
            {
            if (j>maxn)
                break;
            A[j] = false;
            }
        }
    g << c;
    return 0;
}