#include <fstream>
using namespace std;
ifstream f("ciur.in");
ofstream g("ciur.out");
int n, i, j, cnt;
bool w[2000001];
int main()
{
    f >> n;
    for(i = 2; i <= n; ++ i)
        if(w[i] == 0)
    {
        cnt ++;
        for(j = i + i; j <= n; j += i)
            w[j] = 1;
    }
    g << cnt;
    return 0;
}