#include <bits/stdc++.h>
using namespace std;
using i64 = long long;
int Find(i64 n){
    int i = 63;
    while((1LL << i) >= n){
        i--;
    }
    if(i % 2 != 0){
        i--;
    }
    return i;
}
int main(){
    cin.tie(nullptr)->sync_with_stdio(false);
    i64 num;
    cin >> num;
    int result = Find(num);
    cout << result << endl;
    return 0;
}#include <bits/stdc++.h>
using namespace std;
using i64 = long long;
int Find(i64 n){
    int i = 63;
    while((1LL << i) >= n){
        i--;
    }
    if(i % 2 != 0){
        i--;
    }
    return i;
}
int main(){
    cin.tie(nullptr)->sync_with_stdio(false);
    i64 num;
    cin >> num;
    int result = Find(num);
    cout << result << endl;
    return 0;
}