var n,i,j,k,l:longint; a,b:array[1..1000]of longint; q:Array[0..1,0..1010]of longint;
    p:array[0..1]of longint; v:Array[0..1010]of boolean;
function fit(x,y:longint):boolean;
var i,j:longint;
begin
 if y=0 then exit(true); if y=n+1 then exit(true);
 i:=x mod(a[y]+b[y]); if i=0 then exit(false); if i<=a[y] then exit(true) else exit(false);
end;
begin
assign(input,'rivera.in'); assign(output,'rivera.out'); reset(input); rewrite(output);
 readln(n); for i:=1 to n do readln(a[i],b[i]); q[0,0]:=0; p[0]:=1;
 for i:=1 to 10000 do
  begin
   fillchar(v,sizeof(v),false);
   for j:=1 to p[(i+1) and 1] do
    begin
     for k:=q[i and 1,j]-5 to q[i and 1,j]+5 do if k=n+1 then
     begin write(i); close(input); close(output); halt; end else
      if(k>=0)and(k<=n+1)and(fit(i,k))and not(v[k])then
       begin
        inc(p[i and 1]); q[(i+1)and 1,p[i and 1]]:=k; v[k]:=true;
       end;
     p[(i+1)and 1]:=0;
    end;
  end;
 write('NO');  close(input); close(output);
end.