#include <fstream>

using namespace std;

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

bool prim[2000005];

int main()
{
    int i, j,n, cnt=0;
    in>>n;
    for (i = 2; i <= n; i++)
        prim[i] = 1;
    for (i = 2; i <= n; i++)
        if (prim[i])
        {
            ++cnt;
            for (j = i+i; j <= n; j += i)
                prim[j] = 0;
        }
    out<<cnt;
    return 0;
}