#include <fstream>
#include <cstdlib>

using namespace std;

const int NMAX = 2000011;

char isNPrime[NMAX];

int main()
{
    int N, i, j, count, toAdd;
    ifstream in("ciur.in");
    ofstream out("ciur.out");

    in >> N;
    count = (N + 1) >> 1;
    for(i = 1; ((i * i) << 1) + (i << 1) < N; ++i)
    {
        if(isNPrime[i >> 3] & (1 << (i & 7))) continue;
        toAdd = (i << 1) | 1;
        for(j = ((i * i) << 1) + (i << 1); (j << 1) < N; j += toAdd)
        {
            if(0 == (isNPrime[j >> 3] & (1 << (j & 7)))) --count;
            isNPrime[j >> 3] |= 1 << (j & 7);
        }
    }
    out << count << '\n';

    return EXIT_SUCCESS;
}