N, M = map(int, input().split())
S = input()
T = input()

dp = [[float('inf')] * (N + 1) for i in range(M + 1)]

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

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

print(dp[M][N])