using System;
namespace Rextester
{ public class Program
  { public static void Main(string[] args)
    { string s ="0111";
      int n = 0,  p = 1;      
      for (int i = s.Length-1; 0 <= i; i--)
      { if (s[i] == '1') n += p;
        p *= 2;
      }            
      Console.WriteLine(n);
    }
  }
}