```
class Solution:
# @param tokens, a list of string
# @return an integer
def evalRPN(self, tokens):
oper = {
'+':lambda x,y:x+y,
'-':lambda x,y:x-y,
'*':lambda x,y:x*y,
'/':lambda x,y:int(x/y)
}
stk = []
for item in tokens:
if item not in ['+','-','*','/']:
stk.append(int(item))
else:
op2 = stk.pop()
op1 = stk.pop()
stk.append(oper[item](op1,op2))
return stk[0]
```