def min(a,b,c):
    if a>b:
        if b>c:
            return c
        else:
            return b
    else:
        if a>c:
            return c
        else:
            return a

n,m = map(int,input().split())
S=input()
T=input()
inf=float('inf')
a=[]
for i in range(0,n+1):
    a.append([inf]*(m+1))
a[0][0]=0
for i in range(0,n+1):
    for j in range(0,m+1):
        if j==0 and i==0:
            continue
        elif j==0:
            a[i][j]=a[i-1][j]+1
        elif i==0:
            a[i][j]=a[i][j-1]+1
        else:
            if S[i-1]==T[j-1]:
                a[i][j]=a[i-1][j-1]
            else:
                a[i][j]=min(a[i][j-1],a[i-1][j],a[i-1][j-1])+1

print(a[n][m])