为什么错了?求解

var n,m,i,j,x,y,max:longint;
a:array[0..1001]of string;
b,c:array[0..1001]of longint;
s:string;
begin
readln(n,m);
for i:=1 to n do
  begin
  readln(a[i]);
  val(a[i],c[i]);
  b[i]:=length(a[i]);
  end;
for i:=1 to m do
  begin
  readln(x,y);
  str(y,s);
  max:=maxlongint;
  for j:=1 to n do
    if (b[j]>=x) and (c[j]<max) and (pos(s,a[j])=b[j]-x+1) then
      max:=c[j];
  if max=maxlongint then
    writeln(-1)
  else
    writeln(max);
  end;
end.