BZOJ1345: [Baltic2007]序列问题Sequence

 1 var ans:int64;
 2     i,n,x,top:longint;
 3     sta:array[0..1500000] of longint;
 4 procedure main;
 5  begin
 6    readln(n);
 7    sta[0]:=maxlongint;top:=0;ans:=0;
 8    for i:=1 to n do
 9     begin
10       readln(x);
11       while (top>0) and (x>=sta[top]) do
12        begin
13          if x>=sta[top-1] then inc(ans,sta[top-1])
14          else inc(ans,x);
15          dec(top);
16        end;
17       inc(top);sta[top]:=x;
18     end;
19    for i:=1 to top-1 do inc(ans,sta[i]);
20    writeln(ans);
21  end;
22 
23 begin
24   assign(input,‘input.txt‘);assign(output,‘output.txt‘);
25   reset(input);rewrite(output);
26   main;
27   close(input);close(output);
28 end.