#include <fstream>

using namespace std;
ifstream f("ciur.in");
ofstream g("ciur.out");
int n,i,j,p[2000002],s;
int main()
{
    f >> n;
    p[1] = 1;
    s = 1;
    for(i = 3; i <= n; i+=2){
        if(p[i] == 0){
            s++;
            for(j = i + i + i; j <= n; j += i){
                p[j] = 1;

            }
        }
    }
    g << s;
    return 0;
}