program sample
    implicit none
    character(1)::s,t
    integer(8) :: i,j,k,m,n
    integer(8)::a,b,c,d
    integer(8),allocatable::x(:),y(:)
  
    read(*,*) s
   
        if(s.eq. 'T')then
            write(*,*)'A'
        elseif(s.eq. 'A')then
            write(*,*)'T'
        elseif(s.eq. 'C')then
            write(*,*)'G'
        elseif(s.eq. 'G')then
            write(*,*)'C'
        end if
    
    
    stop
end program sample
  

