import sys
input=lambda: sys.stdin.readline().rstrip()
n,m=map(int,input().split())
S=input()
T=input()
DP=[[0]*(m+1) for _ in range(n+1)]
for i in range(n):
  DP[i+1][0]=i+1
for j in range(m):
  DP[0][j+1]=j+1
for i in range(n):
  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+1],DP[i+1][j],DP[i][j])+1
print(DP[n][m])