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))
for a in range(n):
 for b in range(m):d[a+1][b+1]=[1+min(d[a][b],d[a+1][b],d[a][b+1]),d[a][b]][S[a]==T[b]]
print(d[n][m])