#include <fstream>

using namespace std;

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

int v[2000000];
int main()
{
    int n, k = 0, i, j;
    fin >> n;
    if(n <= 1)
        fout << 0;
    else
        for(i = 2; i <= n; i++)
        {
            if(v[i] == 0)
                k++;
            for(j = i * 2; j <= n; j += i)
                v[j] = 1;
        }
    fout << k;
    fin.close();
    fout.close();
    return 0;
}