var
a : array [1..100] of real;
n, i : integer;
begin
read (n);
for i := 1 to n do read (a[i]);
for i := 1 to n do
if a[i] <= 0 then</p>
begin
writeln ('NO');
readln;
Halt;
end;
writeln ('YES');
readln;
end.
var
a : array [1..100] of real;
n, i : integer;
o : real;
begin
read (n);
for i := 1 to n do read (a[i]);
o := a[1];
for i := 2 to n do
if a[i] <> o then
begin
writeln ('NO');
readln;
Halt;
end;
writeln ('YES');
readln;
end.
var
a : array [1..100] of real;
n, i : integer;
x : real;
begin
read (n);
for i := 1 to n do read (a[i]);
read (x);
for i := 1 to n do
if a[i] = x then
begin
writeln ('YES');
readln;
Halt;
end;
writeln ('NO');
readln;
end.