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

INF = 10**3
DP = []
for _ in range(N+1):
    DP.append([INF]*(M+1))
DP[0][0] = 0 
for i in range(N):
    for j in range(M):
        if S[i] == T[j]:
            DP[i+1][j+1] = min(DP[i][j], DP[i+1][j] + 1, DP[i][j+1] + 1)
        else:
            DP[i+1][j+1] = min(DP[i+1][j+1], DP[i][j] + 1, DP[i+1][j] + 1, DP[i][j+1] + 1)
print(DP[N][M])