def diff
  n, m = gets.chomp.split(" ").map(&:to_i)
  s = gets.chomp
  t = gets.chomp
  dp = Array.new(n+1){Array.new(m+1, 0)}

  n.times do |i|
    m.times do |j|
      dp[i+1][j+1] = [dp[i+1][j] + 1 , dp[i][j+1]+1, dp[i][j]].min if s[i] == t[j]
    end
  end
  dp[s][t]
end

puts diff