E

inp = input().split()
stack = []
s = ''
for i in inp:
    if i == '+':
        if len(stack) < 2:
            s = 'ERROR'
            break
        else:
            stack.append(str(int(stack[-2]) + int(stack[-1])))
            stack.pop(-2)
            stack.pop(-2)

    elif i == '-':
        if len(stack) < 2:
            s = 'ERROR'
            break
        else:
            stack.append(str(int(stack[-2]) - int(stack[-1])))
            stack.pop(-2)
            stack.pop(-2)

    elif i == '*':
        if len(stack) < 2:
            s = 'ERROR'
            break
        else:
            stack.append(str(int(stack[-2]) * int(stack[-1])))
            stack.pop(-2)
            stack.pop(-2)

    elif i == '/':
        if len(stack) < 2:
            s = 'ERROR'
            break
        else:
            stack.append(str(int(stack[-2]) // int(stack[-1])))
            stack.pop(-2)
            stack.pop(-2)

    else:
        stack.append(i)

if len(stack) != 1:
    s = 'ERROR'
if s != 'ERROR':
    s = stack[0]
print(s)