give you two integers L<=R, we call a string A "good" if 

1.len(A) > R 

2.there is a string B is both the prefix and suffix of A

3.L <= len(B) <= R

(len(X) means the length of x)

for a give string S, you should find the length of longest good string in all substring of S

if there is no good string,just output 0

the first line contains two integers L, R (L<=R<=1e6)

the second line contains the string S (|S|<=1e6)

output the answer in one line

Sample Input1
2 3
rssrssr

Sample Input2
3 4
rssrssr

Sample Output
6

Sample Output2
7