Write C$++$ code and add input.txt to the code so that I can compile my text.

Consider push and pop operations with the stack. Initially stack in empty. Process all operations. Print the sum of all elements remained in the stack.

If the stack is empty and pop command arrives, do nothing.

Input

Sequence of push and pop operations.

Output

Print the sum of all elements remained in the stack after processing all operations.

Sample input

push $1$

push $2$

pop

push $3$

Sample output

$4$

Explanation

After processing all operations, stack contains numbers $1$ and $3.$ Their sum is $1+3=4.$