# coding:utf-8
#JSRUN引擎2.0,支持多达30种语言在线运行,全仿真在线交互输入输出。
import functools
import sys
# 处理输入
params = [x for x in input().split(" ")]
scores = []
flag = False
for i in range(len(params)):
if (params[i] == "+") :
if len(scores)<2:
print(-1)
flag = True
break
scores.append(scores[len(scores)-2] + scores[len(scores)-1])
elif (params[i] == "D") :
if len(scores)<1:
print(-1)
flag = True
break
scores.append(2*scores[len(scores)-1])
elif (params[i] == "C"):
if len(scores)<1:
print(-1)
flag = True
break
scores.pop()
else:
scores.append(int(params[i]))
if not flag:
print(sum(scores))