#!/usr/bin/env ruby

n, m = gets.split(' ').map &:to_i
S = gets.chomp
T = gets.chomp

# dp[i+1][j+1]: S i文字目までを変換してT[j]にするための手数と定義する
# S: pirikapirirara
# T: poporinapeperuto

dp = []

# Initialization
(0..n).each do |i|
  (0..m).each do |j|
    dp[i] ||= []
    dp[i][j] = j if i == 0
    dp[i][j] = i if j == 0
  end
end

(0...n).each do |i|
  (0...m).each do |j|
    c1 = S[i] == T[j] ? dp[i][j] : dp[i][j] + 1
    c2 = dp[i][j+1] + 1
    c3 = dp[i+1][j] + 1

    dp[i+1][j+1] = [c1,c2,c3].min
  end
end

puts dp[S.length][T.length]