#include <fstream>
using namespace std;

const int NMAX = 2000000;
bool v[NMAX + 1]; /// v[i] = 0 <=> i este prim

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

void ciur(int n)
{
    int i, j;
    v[0] = v[1] = 1;
    for(i = 4; i <= n; i += 2)
        v[i] = 1;
    for(i = 3; i * i <= n; i += 2)
        if(v[i] == 0)
         for(j = i * i; j <= n; j += 2* i)
            v[j] = 1;
}

int main()
{
    int n, x, C = 0;
    ciur(NMAX);
    fin >> n;
    for(int i = 1; i<=n; i++)
    {
        if(v[i] == 0)
            C++;
    }
    fout << C;
    fin.close();
    fout.close();
    return 0;
}