# Exam

Your friend and you took the same true/false exam. You know your answers, your friend’s answers, and the number of your friend’s answers that were correct.

Compute the maximum possible score you could have gotten.

## Input

The first line contains a single integer $k$, the number of correct answers on your friend’s exam.

The second line contains a string of characters, the answers
you wrote down. Each letter is either a ‘`T`’
or an ‘`F`’. The length of the string is the
number $n$ of exam
questions.

The third line also contains a string of $n$ characters, the answers your
friend wrote down. Each letter is either a ‘`T`’ or an ‘`F`’.

Bounds are $0 \leq k \leq n \leq 1\, 000; 1 \leq n$.

## Output

The output is one line containing the maximum number of questions you could have gotten correct.

Sample Input 1 | Sample Output 1 |
---|---|

3 FTFFF TFTTT |
2 |

Sample Input 2 | Sample Output 2 |
---|---|

6 TTFTFFTFTF TTTTFFTTTT |
9 |