import sys
input = sys.stdin.readline

n, m = map(int, input().split())
S = input()[:-1]
T = input()[:-1]
dp = [[0]*(m+1) for _ in range(n+1)]

for i in range(n+1):
    dp[i][0] = i

for i in range(m+1):
    dp[0][i] = i

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

print(dp[n][m])