#!/usr/bin/env python
# -*- coding: utf-8 -*-

n,m = map(int,input().split())
S = input()
T = input()

dp = [[0 for i in range(m + 1)] for j in range(n + 1)]
for i in range(n+1):
    dp[i][0] = i
for i in range(m+1):
    dp[0][i] = i

for i in range(1,n+1):
    for j in range(1,m+1):
        ins = dp[i-1][j] + 1
        Del = dp[i][j-1] + 1
        rev = dp[i-1][j-1] + (1  if S[i-1] != T[j-1] else 0)
        dp[i][j] = min(ins,Del,rev)

print(dp[n][m])