n,m = map(int,input().split())
S = input()
T = input()
DP = [[0]*(m+1) for i in range(n+1)]
DP[0] = [i for i in range(m+1)]
for i in range(n):
    DP[i+1][0] = i+1
    for j in range(m):
        if S[i] == T[j]:
            DP[i+1][j+1] = DP[i][j]
        else:
            DP[i+1][j+1] = min(DP[i][j],DP[i+1][j],DP[i][j+1])+1
print(DP[n][m])