#include <iostream>
#include <fstream>
#include <bitset>

using namespace std;

ifstream f ("ciur.in");
ofstream t ("ciur.out");

long long n;
const int MAX=2000005;
bitset <( MAX>>1 )> v;

long long magic()
{int s=1;
for(int i = 3; i<= n; i += 2){
if(v[i>>1]) continue;
for(int j = i + (i >> 1); j <= n>>1; j += i)
v[j] = 1;
++s;}
return s;
}

int main()
{
    f>>n;
    t<<magic();
    return 0;
}