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

INF = 10**10
DP = []
for _ in range(N+2):
    DP.append([INF]*(M+2))
DP[0][0] = 0 
for i in range(N+1):
    for j in range(M+1):
        if i < N and j < M:
            if S[i] == T[j]:
                DP[i+1][j+1] = min(DP[i+1][j+1], DP[i][j])
            else:
                DP[i+1][j+1] = min(DP[i+1][j+1], DP[i][j] + 1)

        DP[i+1][j] = min(DP[i][j] + 1, DP[i+1][j])
        DP[i][j+1] = min(DP[i][j] + 1, DP[i][j+1])
print(DP[N][M])