AoC 2019 Day2 FORTRAN

PROGRAM DAY2
  INTEGER :: N,NOUN,VERB,IERR
  CHARACTER(1) :: CHAR
  INTEGER, ALLOCATABLE :: PROG(:)

  ! Input
  OPEN(1,FILE="input.txt")
  N=0
  DO
     READ(1,'(A1)',ADVANCE="NO",IOSTAT=IERR)CHAR
     IF(IERR.NE.0)EXIT
     IF(CHAR.EQ.',')N=N+1
  END DO
  ALLOCATE(PROG(0:N))
  REWIND(1)
  READ(1,*)PROG
  CLOSE(1)

  ! Part 1
  WRITE(*,'(A,I0)') "Part 1: ",RUN(PROG,12,02)

  ! PART 2
  OUTER:DO NOUN = 0,99
     DO VERB = 0,99
        IF(RUN(PROG,NOUN,VERB).EQ.19690720)EXIT OUTER
     END DO
  END DO OUTER
  WRITE(*,'(A,2I2.2)') "Part 2: ",NOUN,VERB
  DEALLOCATE(PROG)

CONTAINS
  FUNCTION RUN(IN,NOUN,VERB)
    INTEGER :: IN(:),I,NOUN,VERB,RUN
    INTEGER :: PROG(0:SIZE(IN,DIM=1)-1)
    PROG=IN
    PROG(1:2)=(/NOUN,VERB/)
    I=0
    DO
       SELECT CASE (PROG(I))
       CASE (1)
          PROG(PROG(I+3))=PROG(PROG(I+1))+PROG(PROG(I+2))
       CASE (2)
          PROG(PROG(I+3))=PROG(PROG(I+1))*PROG(PROG(I+2))
       CASE DEFAULT
          EXIT
       END SELECT
       I=I+4
    END DO
    RUN = PROG(0)
  END FUNCTION RUN
END PROGRAM DAY2