gistfile1.f

C FILE: FIB1.F
      PROGRAM FIB1
      INTEGER X
      X = 12
      WRITE(*,*), FIB(X)
      END PROGRAM FIB1

      FUNCTION FIB(N)
C
C     CALCULATE THE NTH FIBONACCI NUMBER
C
      REAL N2, N1, FIB
      N1 = 1.0D0
      N2 = 1.0D0
      DO I=3,N
            FIB = N1 + N2
            N2 = N1
            N1 = FIB
      ENDDO
      RETURN
      END
C END FILE FIB1.F