You are given two strings $s$ and $t$, each of length $n$ and consisting of lowercase Latin alphabets. You want to make $s$ equal to $t$. 

You can perform the following operation on $s$ any number of times to achieve it —   Choose any substring of $s$ and rotate it clockwise once, that is, if the selected substring is $s[l,l+1...r]$, then it becomes $s[r,l,l + 1 ... r - 1]$. All the remaining characters of $s$ stay in their position. 

For example, on rotating the substring $[2,4]$ , string "abcde" becomes "adbce". 

A string $a$ is a substring of a string $b$ if $a$ can be obtained from $b$ by deletion of several (possibly, zero or all) characters from the beginning and several (possibly, zero or all) characters from the end.

Find the minimum number of operations required to convert $s$ to $t$, or determine that it's impossible.


-----Input-----

The first line of the input contains a single integer $t$ $(1\leq t \leq 2000)$ — the number of test cases. The description of the test cases follows.

The first line of each test case contains a single integer $n$ $(1\leq n \leq 2000)$ — the length of the strings. 

The second and the third lines contain strings $s$ and $t$ respectively.

The sum of $n$ over all the test cases does not exceed $2000$.


-----Output-----

For each test case, output the minimum number of operations to convert $s$ to $t$. If it is not possible to convert $s$ to $t$, output $-1$ instead.


-----Example-----
Input
6
1
a
a
2
ab
ba
3
abc
cab
3
abc
cba
4
abab
baba
4
abcc
aabc

Output
0
1
1
2
1
-1



-----Note-----

For the $1$-st test case, since $s$ and $t$ are equal, you don't need to apply any operation.

For the $2$-nd test case, you only need to apply one operation on the entire string ab to convert it to ba.

For the $3$-rd test case, you only need to apply one operation on the entire string abc to convert it to cab.

For the $4$-th test case, you need to apply the operation twice: first on the entire string abc to convert it to cab and then on the substring of length $2$ beginning at the second character to convert it to cba.

For the $5$-th test case, you only need to apply one operation on the entire string abab to convert it to baba.

For the $6$-th test case, it is not possible to convert string $s$ to $t$.

Difficulty: interview

Starter code:

Solutions:
def num(c):
    return ord(c) - 97

import sys
input = sys.stdin.readline

t = int(input())
for _ in range(t):
    n = int(input())
    s1 = input().strip()
    s2 = input().strip()

    char1 = [0] * 26
    char2 = [0] * 26
    for c in s1:
        char1[num(c)] += 1
    for c in s2:
        char2[num(c)] += 1
    if char1 != char2:
        print(-1)
        continue

    dp = [[(False, 0, 0) for j in range(n+1)] for i in range(n + 1)]
    dp[0][0] = [True, 0,[0]*26]

    def upd(a, b, val, sett):
        if not dp[a][b][0] or val > dp[a][b][1]:
            dp[a][b] = (True, val, sett)
    
    for i in range(n):
        for j in range(n):
            valid, val, tab = dp[i][j]
            if not valid:
                continue
            
            top = s1[i]
            bot = s2[j]

            if top == bot:
                #upd(i+1, j+1, val + 1, tab)
                if not dp[i + 1][j + 1][0] or val + 1 > dp[i + 1][j + 1][1]:
                    dp[i + 1][j + 1] = [True, val + 1, tab]

            if tab[num(top)] > 0:
                sett = tab[:]
                sett[num(top)] -= 1
                
                #upd(i+1, j, val, sett)
                if not dp[i + 1][j][0] or val > dp[i + 1][j][1]:
                    dp[i + 1][j] = [True, val, sett]

            sett = tab[:]
            sett[num(bot)] += 1
            #upd(i, j + 1, val, sett)
            if not dp[i][j + 1][0] or val > dp[i][j + 1][1]:
                dp[i][j + 1] = [True, val, sett]

            del dp[i][j][2]

    poss = [dp[i][n][1] for i in range(n + 1)]
        

    print(n - max(poss))
            
    


def num(c):
    return ord(c) - 97

import sys
input = sys.stdin.readline

t = int(input())
for _ in range(t):
    n = int(input())
    s1 = input().strip()
    s2 = input().strip()

    char1 = [0] * 26
    char2 = [0] * 26
    for c in s1:
        char1[num(c)] += 1
    for c in s2:
        char2[num(c)] += 1
    if char1 != char2:
        print(-1)
        continue

    dp = [[(False, 0, 0) for j in range(n+1)] for i in range(n + 1)]
    dp[0][0] = [True, 0,[0]*26]

    def upd(a, b, val, sett):
        if not dp[a][b][0] or val > dp[a][b][1]:
            dp[a][b] = (True, val, sett)
    
    for i in range(n):
        for j in range(n):
            valid, val, tab = dp[i][j]
            if not valid:
                continue
            
            top = s1[i]
            bot = s2[j]

            if top == bot:
                #upd(i+1, j+1, val + 1, tab)
                if not dp[i + 1][j + 1][0] or val + 1 > dp[i + 1][j + 1][1]:
                    dp[i + 1][j + 1] = [True, val + 1, tab]

            if tab[num(top)] > 0:
                sett = tab[:]
                sett[num(top)] -= 1
                
                #upd(i+1, j, val, sett)
                if not dp[i + 1][j][0] or val > dp[i + 1][j][1]:
                    dp[i + 1][j] = [True, val, sett]

            sett = tab[:]
            sett[num(bot)] += 1
            #upd(i, j + 1, val, sett)
            if not dp[i][j + 1][0] or val > dp[i][j + 1][1]:
                dp[i][j + 1] = [True, val, sett]

            del dp[i][j][2]

    poss = [dp[i][n][1] for i in range(n + 1)]
        

    print(n - max(poss))
            


def num(c):return ord(c) - 97
import sys
input = sys.stdin.readline
for _ in range(int(input())):
    n = int(input());s1 = input().strip();s2 = input().strip();char1 = [0] * 26;char2 = [0] * 26
    for c in s1:char1[num(c)] += 1
    for c in s2:char2[num(c)] += 1
    if char1 != char2:print(-1);continue
    dp = [[(False, 0, 0) for j in range(n+1)] for i in range(n + 1)];dp[0][0] = [True, 0,[0]*26]
    def upd(a, b, val, sett):
        if not dp[a][b][0] or val > dp[a][b][1]:dp[a][b] = (True, val, sett)    
    for i in range(n):
        for j in range(n):
            valid, val, tab = dp[i][j]
            if not valid:continue            
            top = s1[i];bot = s2[j]
            if top == bot:
                if not dp[i + 1][j + 1][0] or val + 1 > dp[i + 1][j + 1][1]:dp[i + 1][j + 1] = [True, val + 1, tab]
            if tab[num(top)] > 0:
                sett = tab[:];sett[num(top)] -= 1
                if not dp[i + 1][j][0] or val > dp[i + 1][j][1]:dp[i + 1][j] = [True, val, sett]
            sett = tab[:];sett[num(bot)] += 1
            if not dp[i][j + 1][0] or val > dp[i][j + 1][1]:dp[i][j + 1] = [True, val, sett]
            del dp[i][j][2]
    poss = [dp[i][n][1] for i in range(n + 1)]        
    print(n - max(poss))

def read_int():
    return int(input())


def read_ints():
    return list(map(int, input().split(' ')))


t = read_int()
for case_num in range(t):
    n = read_int()
    cnt = [0 for i in range(26)]
    ps = [[0 for j in range(n + 1)] for i in range(26)]
    pt = [[0 for j in range(n + 1)] for i in range(26)]
    s = input()
    t = input()
    for i in range(n):
        ch = ord(s[i]) - ord('a')
        cnt[ch] += 1
        for j in range(26):
            ps[j][i + 1] = ps[j][i] + (1 if ch == j else 0)
    for i in range(n):
        ch = ord(t[i]) - ord('a')
        cnt[ch] -= 1
        for j in range(26):
            pt[j][i + 1] = pt[j][i] + (1 if ch == j else 0)
    ok = True
    for i in cnt:
        if i != 0:
            ok = False
            break
    if not ok:
        print(-1)
    else:
        r = n
        while r >= 1 and s[r - 1] == t[r - 1]:
            r -= 1
        inf = int(1e8)
        dp = [[0 if i == 0 else inf for j in range(
            r + 1)] for i in range(r + 1)]
        for i in range(1, r + 1):
            for j in range(i, r + 1):
                if s[i - 1] == t[j - 1]:
                    dp[i][j] = min(dp[i][j], dp[i - 1][j - 1])
                ch = ord(t[j - 1]) - ord('a')
                if ps[ch][r] - ps[ch][i] > pt[ch][r] - pt[ch][j]:
                    dp[i][j] = min(dp[i][j], dp[i][j - 1])
                dp[i][j] = min(dp[i][j], dp[i - 1][j] + 1)
        print(dp[r][r])


import sys

int1 = lambda x: int(x) - 1
p2D = lambda x: print(*x, sep="\n")
def II(): return int(sys.stdin.readline())
def MI(): return map(int, sys.stdin.readline().split())
def LI(): return list(map(int, sys.stdin.readline().split()))
def LLI(rows_number): return [LI() for _ in range(rows_number)]
def SI(): return sys.stdin.readline()[:-1]

def main():
    inf=10**9
    for _ in range(II()):
        n=II()
        s = SI()
        t = SI()

        cnts=[[0]*26 for _ in range(n+1)]
        cntt=[[0]*26 for _ in range(n+1)]
        for i in range(n-1,-1,-1):
            cnts[i][ord(s[i])-97]+=1
            cntt[i][ord(t[i])-97]+=1
            for j in range(26):
                cnts[i][j]+=cnts[i+1][j]
                cntt[i][j]+=cntt[i+1][j]

        ng=False
        for j in range(26):
            if cnts[0][j]!=cntt[0][j]:
                ng=True
                break
        if ng:
            print(-1)
            continue

        dp=[[inf]*(n+1) for _ in range(n+1)]
        for i in range(n+1):dp[i][0]=0
        for i in range(n+1):
            for j in range(i,n+1):
                if i==n and j==n:break
                pre=dp[i][j]
                if pre==inf:continue
                if i<j and i+1<=n:dp[i+1][j]=min(dp[i+1][j],pre+1)
                if i+1<=n and j+1<=n and s[i]==t[j]:dp[i+1][j+1]=min(dp[i+1][j+1],pre)
                if j+1<=n and cnts[i+1][ord(t[j])-97]>cntt[j+1][ord(t[j])-97]:
                    dp[i][j + 1] = min(dp[i][j + 1], pre)
        #p2D(dp)
        print(dp[n][n])

main()