program test
implicit none
character::S*4
read*,S
if('S(1:1)'=='S(2:2)' .and. 'S(3:3)'=='S(4:4)' .and. 'S(1:1)'/='S(3:3)') then 
print*,'Yes'
else if ('S(1:1)'=='S(3:3)' .and. 'S(2:2)'=='S(4:4)' .and. 'S(2:2)'/='S(3:3)') then
print*,'Yes'
else if('S(1:1)'=='S(4:4)' .and. 'S(3:3)'=='S(2:2)' .and. 'S(1:1)'/='S(3:3)') then
print*,'Yes'
else 
print*,'No'
end if
end program test