class Yukicoder
  def initialize
    n, m = gets.chomp.split.map(&:to_i)
    s = gets.chomp
    t = gets.chomp
    dp = Array.new(n+1){ Array.new(m+1, [n,m].max)}

    dp[0][0] = 0

    1.upto(n) do |i|
      1.upto(m) do |j|
        if s[i-1] == t[j-1]
          dp[i][j] = [dp[i][j], dp[i-1][j-1]].min
        else
          dp[i][j] = [dp[i][j], dp[i-1][j]+1].min
          dp[i][j] = [dp[i][j], dp[i][j-1]+1].min
          dp[i][j] = [dp[i][j], dp[i-1][j-1]+1].min
        end
      end
    end

    p dp[n][m]
  end
end

Yukicoder.new