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What will I learn?

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Statement

 Goal

You are given a row of N light bulbs, represented by a string of 0 or 1, totally N characters in the string.
0 means the light bulb is OFF.
1 means the light bulb is ON.

The left-most character is light bulb 1.
The right-most character is light bulb N.

Each light bulb has an independent switch allowing you to switch it ON or OFF.

To switch ON/OFF any light bulb, there are two rules:

Rule 1 You can change the state of light bulb i if i+1 is ON AND i+2, i+3,... N are OFF.
Rule 2 Rule 1 does not apply to light bulb N, which can be switched ON/OFF at will.

The game starts with a given lighting pattern.
You will also have a target lighting pattern.

Find the minimum number of switches needed to change the pattern from start to target.


Example
To change pattern from 1101 to 0100

1101 (start)
1100 (switch #4, by Rule 2)
0100 (switch #1, by Rule 1) - reached target by switching 2 times.
Input
Line 1: Start pattern - a string of 0 or 1, totally N characters
Line 2: Target pattern - a string of 0 or 1, totally N characters
Output
Line 1: The minimum number of switching needed to change the lighting pattern from start to target.
Constraints
1 ≤ N ≤ 25
Example
Input
1101
0100
Output
2
Solve it

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