#include <fstream>

using namespace std;

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

int n,i,j,contor;

bool v[2000007];

int main()
{
    fin>>n;

    for (i = 2; i <= n; i++)
        v[i] = 1;

    for (i = 2; i <= n; i++)
        if (v[i])
        {
            contor++;
            for (j = i+i; j <= n; j += i)
                v[j] = 0;
        }
    fout<<contor<<'\n';
    return 0;
}