Beleg/tt.py

def toList(s):

    L = []
    for i in s:
        if i != '\n':
            L.append(i)
    return L

def f(i,s,S = None):
    
    if not S:
        S = []
        
    if i == len(s):
        return S[0]

    a = s[i]
    if a.isdigit():
        S.append(a)
        return f(i+1,s,S)
    else:
        c = S.pop()
        d = S.pop()
        e = '%s%s%s'%(c,a,d)
        S.append(eval(e))
        return f(i+1,s,S)

x = raw_input()
s = ""
while x != '=\n':
    s += x
    x = raw_input() + '\n'

print f(0,toList(s))