#include <fstream>

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