n,m=map(int,input().split())
S=input()
T=input()
d=[[i]+[-1]*m for i in range(n+1)]
d[0]=list(range(m+1))
def f(a,b):
 global d
 if d[a][b]>=0:return d[a][b]
 t=f(a-1,b-1) if S[a-1]==T[b-1] else 1+min(f(a-1,b-1),f(a,b-1),f(a-1,b))
 d[a][b]=t
 return t
print(f(n,m))