#include <fstream>

using namespace std;

const int NMAX = 2000005;

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

int main()
{
    int n; bool ciur[NMAX] = {0};
    int ct = 0;
    fin >> n;

    for(int i = 2; i <= n; i++)
        if(!ciur[i])
        {
            ct++;
            for(int j = i * i; j <= n; j += i)
                ciur[j] = 1;
        }

    fout << ct;
    return 0;
}