import sys
input = sys.stdin.readline
sys.setrecursionlimit(10**7)

n, m = map(int, input().split())
s = input().rstrip()
t = input().rstrip()
dp = [[0]*(m+1) for _ in range(n+1)]
for i in range(n):
  dp[i+1][0] = dp[i][0]+1
for i in range(m):
  dp[0][i+1] = dp[0][i] + 1
for i in range(n):
  for j in range(m):
    if s[i] == t[j]:
      dp[i+1][j+1] = min(dp[i+1][j]+1, dp[i][j+1]+1, dp[i][j])
    else:
      dp[i+1][j+1] = min(dp[i+1][j]+1, dp[i][j+1]+1, dp[i][j]+1)
      
print(dp[n][m])