s = '1 2 + 5 4 - *'
L = s.split()
print L

def f(i,s,S=[]):
    if i==len(s):
        return S

    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)

print f(0,L)