Program Task_5;
Var
a : array [1..10000] of integer;
i,n, sum: integer;
check : boolean;
Begin
sum:=0;
read(n);
check:=false;
for i := 1 to n do
       read(a[i]);
for i := 1 to n-1 do
    if (a[i+1] = a[i]) then
          check := true;

if (check = true) then
   write('YES')
else
   write('NO');
End.