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using System;
using System.Linq;
using System.Collections.Generic;
using System.Numerics;

namespace ExamPreparation
{
    public sealed class Preparation
    {
        public static void Main()
        {
            string[] tokens = Console.ReadLine().Split();

            int baseN = int.Parse(tokens[0]);
            string number = tokens[1];
            string digits = "0123456789ABCDEF";
            int power = number.Length - 1;
            BigInteger sum = 0;

            for (int i = 0; i < number.Length; i++)
            {
                char currentDigit = number[i];
                int index = digits.IndexOf(currentDigit);
                BigInteger raisedPower = BigInteger.Pow(baseN, power);
                sum += index * raisedPower;

                power--;
            }

            Console.WriteLine(sum);
        }
    }
}