#include <fstream>
#define ll long long
using namespace std;

ifstream f("ciur.in");
ofstream g("ciur.out");
ll n,v[2000001], sol;

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

int main()
{
    f>>n;
    ciur();
    v[1]= 1;
    for( int i = 1; i<= n; ++i) if(v[i] == 0 ) sol++;

    g << sol;
    return 0;
}