#include <fstream>

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

int prim[2000005];

int main()
{
    int N,i,j,c=1;
    in>>N;

    for (i = 3; i <= N; i=i+2)
        if (prim[i]==0)
        {
            c++;
            for (j = i+i+i; j <= N; j=j+i)
                prim[j] = 1;
        }
    out<<c;
    return 0;
}