give string s represents expression evaluate expression return value the integer division truncate zeroyou assume give expression valid all intermediate result range 231 231 1note you allow use builtin function evaluate string mathematical expression eval Example 1input s 322output 7example 2input s 32 output 1example 3input s 35 2 output 5 constraints1 slength 3 105s consist integer operator separate number spacess represent valid expressionall integer expression nonnegative integer range 0 231 1the answer guarantee fit 32bit integer