const
    MAX_N = 1010101;
    MAX_K = 101010;

var
    dp: array[0..1, 0..MAX_N] of integer;
    f: text;

begin
    Assign(f, '27-110b.txt');
    reset(f);

    var N, K : integer;
    readln(f, N, K);

    for var j := 0 to K do
        dp[0][0] := 0;

    var t := 0;
    var nt := 1;

    for var i := 1 to N do
    begin
        var a, b: integer;
        readln(f, a, b);
        dp[nt][0] := dp[t][0];
        for var j := 1 to K do
        begin
            dp[nt][j] := max(dp[t][j], dp[t][j - 1] + a);
            dp[nt][0] := max(dp[nt][0], dp[t][j] + b);
        end;
        swap(t, nt);
    end;

    var ans := -1000000000;

    for var j := 0 to K do
        ans := max(ans, dp[t][j]);

    writeln(ans);
  
end.