#!/usr/bin/env python3
# %%
import sys
read = sys.stdin.buffer.read
readline = sys.stdin.buffer.readline
readlines = sys.stdin.buffer.readlines


# %%
N, M = map(int, readline().split())
S = '~' + readline().rstrip().decode()
T = '~' + readline().rstrip().decode()

# %%
dp = [[0] * (M + 1) for _ in range(N + 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):
        dp[i][j] = min(dp[i - 1][j] + 1, dp[i][j - 1] + 1, dp[i - 1][j - 1] + 1 - (S[i] == T[j]))

print(dp[-1][-1])