N,M = list(map(int, input().split(' ')))
S = input()
T = input()

dp = []
for _ in range(N+1):
    dp.append([0 for _ in range(M+1)])

for i in range(N+1):
    dp[i][0] = i
    
for j in range(M+1):
    dp[0][j] = j

for i in range(1,N+1):
    for j in range(1,M+1):
        cost = 0 if S[i-1] == T[j-1] else 1
        dp[i][j] = min(dp[i-1][j] + 1, dp[i][j-1] + 1, dp[i-1][j-1] + cost)

print(dp[N][M])