# This program converts a numeric string (in given base)
# to a decimal number (base 10). The range for the base
# is limited to 2 <= base <=16

# Also error-checking is done

# exercises 5.26 and 5.35

# prints the quick description of the program
def greetings():
    print 'Greetings!'
    print 'This program converts a numeric string (in given base)'
    print 'to a decimal number (base 10).\n The range for the base',
    print 'is limited to 2 <= base <=16'

# get the data and make sure that the user input
# correct data
def get_data():
    while True:
        base=input('Please, input the base (whole number between 2 and 16, including):')
        if 2<=base<=16:
            break
        else:
            print 'The base is incorrect. It should be between 2 and 16, including'

    flag=0
    while flag==0:
        
        numberString=raw_input('Please, input the number string:')

        flag=1
        for c in numberString:
            if not c.isdigit():
                if ord(c)-87 >= base:
                    flag = 0
                    break
            else:
                if int(c) >= base:
                    flag = 0
                    break
        if flag==0:
            print 'The number string contains illegal characters.'

    return base,numberString.lower()

# make conversion
def convert(b,s):
    string=s[::-1]

    n=len(string)

    sum_=0
    i=0
    for c in string: # iterate over elements of the number string
        if c.isdigit(): # check if c is a digit
            n=int(c)
        else: # if c is not a digit
            n=ord(c)-87
        sum_ += n*(b**i)
        i +=1

    return sum_        
        

def main():

    greetings() # prints the quick description of the program

    # get the data and make sure that the user input
    # correct data
    b,s=get_data() 

    # make conversion
    d=convert(b,s)

    #display the result
    print '%s_%d = %d_10' % (s,b,d)

main()