import sys

sys.setrecursionlimit(10000)
N, M = map(int, raw_input().split())
s1, s2 = raw_input(), raw_input()

mem = {}
def rec(n, m):
    if (n, m) in mem:
        return mem[(n, m)]
    if n == m == -1:
        return 0
    if n == -1:
        return m+1
    if m == -1:
        return n+1
    mem[(n, m)] = min(rec(n-1, m)+1, rec(n, m-1)+1, rec(n-1, m-1)+(s1[n]!=s2[m]))
    return mem[(n, m)]

print rec(N-1, M-1)