nm = input().rstrip().split()
n, m = int(nm[0]), int(nm[1])
S = input().rstrip()
T = input().rstrip()
dp = [[0 for j in range(n+1)] for i in range(m+1)]
for i in range(m+1):
    dp[i][0] = i
for j in range(n+1):
    dp[0][j] = j
# dp[i][j]: Sのj文字目までをTのi文字目までに変換するための最小操作回数
for i in range(m):
    for j in range(n):
        if T[i] == S[j]:
            x = 0
        else:
            x = 1
        dp[i+1][j+1] = min(dp[i][j+1]+1, dp[i+1][j]+1, dp[i][j]+x)
print(dp[m][n])