#include <iostream>
#include <fstream>
using namespace std;

bool c[2000005];
int main()
{
    ifstream f("ciur.in"); ofstream g("ciur.out");
    int nr,n,i,j;
    f>>n;
    nr = 1;
    for(i = 3; i <= n; i += 2)
    {
        c[i] = 1;
    }
    for(i = 3; i <= n; i +=2)
    {
        if(c[i])
        {
            ++nr;
            for(j = i * i; j <= n; j += i)
            {
                c[j] = 0;
            }
        }
    }
    g<<nr;
    return 0;
}