n, m = map(int, input().split())
s = input()
t = input()
INF = 10**18

DP = [[INF for _ in range(m + 1)] for _ in range(n + 1)]
DP[0][0] = 0
for i in range(n):
    for j in range(m):
        DP[i + 1][j] = min(DP[i + 1][j], DP[i][j] + 1)
        DP[i][j + 1] = min(DP[i][j + 1], DP[i][j] + 1)
        if s[i] == t[j]:
            DP[i + 1][j + 1] = min(DP[i + 1][j + 1], 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])