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

INF = 10**10
DP = []
for _ in range(N+1):
    DP.append([INF]*(M+1))
DP[0][0] = 0 

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

        if i > 0:
            DP[i][j] = min(DP[i-1][j] + 1, DP[i][j])
        if j > 0:
            DP[i][j] = min(DP[i][j-1] + 1, DP[i][j])

print(DP[N][M])