n, m = map(int, input().split())
S = input()
T = input()
dp = [[0]*m for _ in range(n)]
dp[0][0] = 1 if S[0]!=T[0] else 0

for i in range(n):
    for j in range(m):
        if i==0 and j==0:
            continue
        elif i==0:
            dp[i][j] = dp[i][j-1]+1
        elif j==0:
            dp[i][j] = dp[i-1][j]+1
        else:
            dp[i][j] = min(dp[i][j-1]+1, dp[i-1][j]+1, dp[i-1][j-1]+(1 if S[i]!=T[j] else 0))

print(dp[n-1][m-1])