#include <fstream>
#include <bitset>
#define in "ciur.in"
#define out "ciur.out"
#define N 2000003

using namespace std;

ifstream fin(in);
ofstream fout(out);

bitset<N> f;

int n;

void Ciur(int n)
{
    f[0] = f[1] = 1;
    for(int i=4; i<=n; i+=2)
        f[i] = 1;
    for(int i=3; i*i<=n; i+=2)
        if(!f[i])
            for(int d=i*i; d<=n; d += 2*i) f[i] = 1;
}

int Solve()
{
    int rez = 0;
    for(int i=2; i<=n; ++i)
        if(!f[i]) ++rez;
    return rez;
}

int main()
{
    fin>>n;

    Ciur(n);

    fout<<Solve();

    fin.close(); fout.close();
    return 0;
}