program project1;
var a,b:array[-10..1050] of longint;
    f:array[0..1,-10..1050] of boolean;
    n:longint;
procedure init;
var i:longint;
begin
     assign(input,'rivera.in ');reset(input);
     assign(output,'rivera.out');rewrite(output);
     read(n);
     for i:=1 to n do
         read(a[i],b[i]);
end;
procedure main;
var t,i,ii,j,k,ll:longint;
begin
     f[0,0]:=true;t:=0;
     while true do
     begin
          inc(t);if t>10000 then begin writeln('NO');halt;end;
          i:=t and 1;ii:=(t+1)and 1;
          for j:=0 to n+1 do
          begin
               if not((j=0)or(j=n+1)) then
               k:=t mod (a[j]+b[j]);
               if (k>=1)and(k<=a[j])or((j=0)or(j=n+1)) then
               begin
                    f[i,j]:=false;
                    for ll:=j-5 to j+5 do
                    begin
                         if ll<0 then continue;
                         if ll>n+1 then break;
                         if f[ii,ll] then begin f[i,j]:=true;break;end;
                    end;
               end else f[i,j]:=false;
          end;
          if f[i,n+1] then
          begin
               writeln(t);
               halt;
          end;
     end;
     close(input);
     close(output);
end;
begin
     init;
     main;
end.