n, m = map(int, input().split(' '))
S = input()
T = input()
# n * mの配列を作成
d = [[None for i in range(m+1)] for j in range(n+1)]

d[0] = list(range(m + 1))

for i in range(1, n + 1):
    d[i][0] = i 
    for j in range(1, m + 1):
        if S[i-1] == T[j-1]:
            d[i][j] = min(d[i][j-1] + 1, d[i-1][j] + 1, d[i-1][j-1])
        else:
            d[i][j] = min(d[i][j-1], d[i-1][j], d[i-1][j-1]) + 1

print(d[n][m])