n,m,s,t = open(0).read().split()
n,m = int(n), int(m)
INF = 1<<30
dp = [[INF]*(m+1) for _ in range(n+1)]
dp[0][0] = 0
for i in range(n+1):
    for j in range(m+1):
        if i: dp[i][j] = min(dp[i][j], dp[i-1][j]+1)
        if j: dp[i][j] = min(dp[i][j], dp[i][j-1]+1)
        if i and j: dp[i][j] = min(dp[i][j], dp[i-1][j-1] + (0 if s[i-1]==t[j-1] else 1))
print(dp[n][m])