local mmi, mma = math.min, math.max
local n, m = io.read("*n", "*n", "*l")
local str = io.read()
local a = {}
for i = 1, n do
  a[i] = str:byte(i)
end
str = io.read()
local b = {}
for i = 1, m do
  b[i] = str:byte(i)
end
local inf = 1000000007
local t = {}
for i = 1, n + 1 do
  t[i] = {}
  for j = 1, m + 1 do
    t[i][j] = inf
  end
end
t[1][1] = 0
for i = 1, n + 1 do
  local num_i = a[i]
  for j = 1, m + 1 do
    local tij = t[i][j]
    local num_j = b[j]
    if j < m + 1 then
      t[i][j + 1] = mmi(t[i][j + 1], 1 + tij)
    end
    if i < n + 1 then
      t[i + 1][j] = mmi(t[i + 1][j], 1 + tij)
    end
    if j < m + 1 and i < n + 1 then
      local cost = 1
      if num_i and num_i == num_j then
        cost = 0
      end
      t[i + 1][j + 1] = mmi(t[i + 1][j + 1], cost + tij)
    end
  end
end
for i = 1, n + 1 do
  -- print(table.concat(t[i], " "))
end
print(t[n + 1][m + 1])