program energii;
var a,b:array[1..5000]of longint;
    g,w,i,j,x,y,min:longint;
    fin,fout:text;

begin
assign(fin,'energii.in'); reset(fin);
assign(fout,'energii.out'); rewrite(fout);

readln(fin,g);
readln(fin,w);

for i:=1 to w+1 do begin
                   a[i]:=-1;
                   b[i]:=-1;
                   end;
for i:=1 to g do begin
    readln(fin,x,y);
    for j:=1 to x do
        if (a[j]<y)and(a[j]<>-1) then b[j]:=a[j]
                                 else b[j]:=y;
    for j:=x+1 to w do
        if (a[j-x]=-1)and(a[j]=-1) then b[j]:=-1
        else begin

        if a[j-x]+y < a[j] then begin
           if a[j-x]<>-1 then b[j]:=a[j-x]+y
                         else b[j]:=-1
        end else begin
           if a[j]=-1 then b[j]:=a[j-x]+y
                      else b[j]:=a[j]
        end;
        end;

    min:=maxlongint;
    for j:=w-x+1 to w do
        if (a[j]<min)and(a[j]<>-1) then min:=a[j];

    if min=maxlongint then b[w+1]:=-1
    else begin
         if (min+y<=a[w+1]) then b[w+1]:=min+y
         else
             if a[w+1]=-1 then b[w+1]:=min+y
                          else b[w+1]:=a[w+1];
         end;

    a:=b;
    {for j:=1 to w+1 do write(fout,a[j],' ');
    writeln(fout);}
end;

if a[w]<a[w+1] then writeln(fout,a[w])
               else writeln(fout,a[w+1]);
close(fin); close(fout);
end.