def diff
  n, m = gets.chomp.split(" ").map(&:to_i)
  s = gets.chomp
  t = gets.chomp
  inf = 100000007
  dp = Array.new(n+2){Array.new(m+2, inf)}
  dp[0][0] = 0

  0.upto n do |i|
    0.upto m do |j|
      dp[i+1][j+1] = s[i] == t[j] ? [dp[i+1][j+1], dp[i][j]].min : [dp[i+1][j+1], dp[i][j]+1 ].min
      dp[i+1][j] = [dp[i+1][j], dp[i][j]+1].min
      dp[i][j+1] = [dp[i][j+1], dp[i][j]+1].min
    end
  end

  dp[n][m]
end

puts diff