power1.pas

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program E1_10a; {power}
var d,p:array[1..10000] of integer;
    n,c,i,t,min,w:longint;

procedure search(left,right,c:integer);
begin
 if (left=0) and (right=n+1) then if w<min then min:=w else
  else
   begin
    if left>0 then
     begin
      t:=t+d[c]-d[left]; w:=w+p[left]*t;
      if w<min then search(left-1,right,left);
      w:=w-t*p[left]; t:=t-d[c]+d[left];
     end;
    if right<n+1 then
     begin
      t:=t+d[right]-d[c]; w:=w+p[right]*t;
      if w<min then search(left,right+1,right);
      w:=w-t*p[right]; t:=t-d[right]+d[c];
     end;
   end
end;

begin {main}
 assign(input,'power.in');reset(input); readln(n,c);
 for i:=1 to n do readln(d[i],p[i]);
 close(input);
 min:=maxlongint; t:=0;
 search(c-1,c+1,c);
 assign(output,'power.out'); rewrite(output);
 writeln(min); close(output)
end.