#include<bits/stdc++.h>
using namespace std;
#define MOD 1000000007
#define LL long long
#define out(x) cout << #x << " : " << x << "\n";

int main() {
   ios_base::sync_with_stdio(false); cin.tie(NULL);
   LL n; cin >> n;
   LL k = floor(log10(n)) + 1;
   LL p = pow(10, k);
   double p2 = 1.0;
   for(LL i = 0;i <= 100000000;i++) {      
      while(p2 >= p) p2 /= 10;
      if((LL)(p2) == n) {
         cout << i << endl;
         return 0;
      }
      p2 = p2 * 2ll;
   }
   cout << -1 << endl;
   return 0;               
}