import sys
input = sys.stdin.readline
sys.setrecursionlimit(10 ** 7)

n, m = map(int, input().split())
S = input().strip()
T = input().strip()

INF = float('inf')

# dp[i+1][j+1]: S[i]/T[j]までの最少コスト(S, Tは0オリジン)
dp = [[INF] * (len(T) + 1) for _ in range((len(S) + 1))]

# 初期条件
dp[0][0] = 0
# 計算量が許すならば、自明な値はfor文を別にすると考えやすい
for i in range(len(S)):
    dp[i+1][0] = dp[i][0] + 1
for j in range(len(T)):
    dp[0][j+1] = dp[0][j] + 1

# 漸化式
for i in range(len(S)):
    for j in range(len(T)):
        if S[i] == T[j]:
            dp[i+1][j+1] = min(dp[i][j], dp[i+1][j] + 1, dp[i][j+1] + 1)
        else:
            dp[i+1][j+1] = min(dp[i][j] + 1, dp[i+1][j] + 1, dp[i][j+1] + 1)

# 求める値
print(dp[len(S)][len(T)])