var
 a,b:array[0..1010]of longint;
 f:array[0..2000,0..1010]of boolean;
 i,j,k,l,m,n,time,p:longint;

function min(a,b:longint):longint;
 begin
  if a<b then exit(a) else exit(b);
 end;

function max(a,b:longint):longint;
 begin
  if a>b then exit(a) else exit(b);
 end;

begin
 assign(input,'rivera.in');reset(input);
 assign(output,'rivera.out');rewrite(output);
 read(n);
 fillchar(a,sizeof(a),1);
 for i:=1 to n do read(a[i],b[i]);
 fillchar(f,sizeof(f),false);
 f[0,0]:=true;
 p:=0;
 while true do
  begin
   inc(p);
  // writeln(p);
   for i:=0 to n+5 do 
    if (p mod (a[i]+b[i])>0)and(p mod (a[i]+b[i])<=a[i]) then 
     begin
      f[p,i]:=false;
      for j:=max(0,i-5) to min(n+1,i+5) do
       if ((p-1) mod (a[j]+b[j])>0)and((p-1) mod (a[j]+b[j])<=a[j]) or (p-1=0) then
        begin
         f[p,i]:=f[p,i] or f[p-1,j];
         if i>=n+1 then
          if f[p,i] then 
           begin
            writeln(p);
            close(input);close(output);
            halt;
           end;
         if f[p,i] then break;
        end;
      end;
   if p>1000 then break;
  end;
 writeln('NO');
 close(input);close(output);
end.