program MIDI;
uses crt;
var i,n :integer; A:array[1..100] of integer; KT: boolean;
begin
clrscr;
write('Nhap so n: ');readln(n);
For i:=1 to n do
begin
write('A[',i,']= ');
readln(A[i]);
end;
For i:=2 to n-1 do
if (A[i+1]>A[i]) and (A[i+2]<A[i+1]) then KT:=true;
For i:=2 to n-1 do
if (A[i+1]<=A[i])and (A[i+2]>=A[i+1]) then
begin
KT:=false;
break;
end;
if KT=true then write('YES');
if KT=false then write('NO');
readln;
end.