How to define path for input file and out file - fortran

Question

How to define input path and output path (Both are different location) and input file name and output file name will be same?
I want to add input and output directory to take and save input and output on respective directory but input and output file name will be same.
Simply, I want to make modification of my code to take input files from input directory folder and save output on output directory folder.
Now my code is working but at a time only one file taking, I want to run my same code for multiple files.
Source:
IMPLICIT DOUBLE PRECISION (A-H,O-Z)
c
c iaa: residue name
c iat: atom name
CHARACTER iaa*4,iat*4,chain*1
DIMENSION iaa(199),iat(199),chain(199)
c
c xpr,ypr,zpr: orthogonal coordinates
c irn: residue number
DIMENSION xpr(199),ypr(199),zpr(199),irn(199),taa(5)
c
c set pi value and rad to deg conversion factor
pi = 0.4D+01*DATAN(0.1D+01)
rad2deg = 0.18D+03/pi
deg2rad = pi/0.18D+03
c
fprec = 2.0*(sin(36.0*deg2rad)+sin(72.0*deg2rad))
c
c open the input file
OPEN (1,FILE="1e3i_A.txt")
c
c read the xyzs, atom and res name and res #
i = 1
396 READ (1,500,END=398) iat(i),iaa(i),chain(i),irn(i),xpr(i),
1 ypr(i),zpr(i)
c WRITE(*,500) iat(i),iaa(i),chain(i),irn(i),xpr(i),ypr(i),zpr(i)
i = i+1
c
c ensure arrays do not overflow
IF (i .GT. 199) THEN
WRITE(*,618)
STOP
ENDIF
c
c loop back and read the next atom entry
GO TO 396
c
c set the number of atoms, nat; close input file
398 nat = i-1
IF (nat .NE. 40) THEN
WRITE(*,632) nat
STOP
ENDIF
CLOSE(1)
c
c open output file
OPEN (3,FILE="output.dat")
c
c loop over all atoms; first get B of A-B-C-D
c
c irt = count of ring torsion angles
irt = 0
DO 716 i1 = 1,nat,4
j1 = i1
j2 = i1+1
j3 = i1+2
j4 = i1+3
c
c calculate the relevant vectors: j1-j2, j2-j3, j3-j4
d11 = xpr(j2) - xpr(j1)
d12 = ypr(j2) - ypr(j1)
d13 = zpr(j2) - zpr(j1)
d21 = xpr(j3) - xpr(j2)
d22 = ypr(j3) - ypr(j2)
d23 = zpr(j3) - zpr(j2)
d31 = xpr(j4) - xpr(j3)
d32 = ypr(j4) - ypr(j3)
d33 = zpr(j4) - zpr(j3)
c
c normals to j1-j2-j3 AND j2-j3-j4
c cross product of j1-j2 and j2-j3 AND of j2-j3 and j3-j4
p1 = d12*d23 - d13*d22
p2 = d13*d21 - d11*d23
p3 = d11*d22 - d12*d21
q1 = d22*d33 - d23*d32
q2 = d23*d31 - d21*d33
q3 = d21*d32 - d22*d31
c
c calculate cos-of-TA: angle between vectos p and q
ta = (p1*q1+p2*q2+p3*q3)/(dsqrt(p1*p1+p2*p2+p3*p3)*
1 dsqrt(q1*q1+q2*q2+q3*q3))
IF (DABS(ta) .GT. 1.0) ta = 1.0
c
c calculate magnitude of TA and convert to degrees
c ta = DACOS(ta)*rad2deg
ta = DACOS(ta)
c
c find sign of TA: find cross product of p and q
x1 = p2*q3 - p3*q2
y1 = p3*q1 - p1*q3
z1 = p1*q2 - p2*q1
c
c if not a null vector, find if parallel to j2-j3 or antiparallel
IF (DABS(x1)+DABS(y1)+DABS(z1) .NE. 0.0) THEN
xx = x1*d21 + y1*d22 + z1*d23
IF (xx .LT. 0.0) ta = -ta
ENDIF
irt = irt+1
taa(irt) = ta
IF (irt .EQ. 5) THEN
fnum = taa(5)+taa(2)-taa(4)-taa(1)
fden = fprec*taa(3)
tanp = fnum/fden
phase = DATAN(tanp)*rad2deg
IF (taa(3) .LT. 0) phase = phase+180.0
IF (phase .LT. 0) phase = phase+360.0
WRITE(*,624) phase
irt = 0
ENDIF
c
c output the value
c WRITE(3,606) iat(j1),irn(j1),iat(j2),irn(j2),iat(j3),
c 2 irn(j3),iat(j4),irn(j4),ta
716 CONTINUE
c
c close output file and exit
CLOSE(3)
c WRITE(*,620)
c
STOP
500 FORMAT(13X,2A4,A1,I4,4X,3F8.3)
502 FORMAT(A20)
606 FORMAT(1X,A4,I4,'... ',A4,I4,'... ',A4,I4,'... ',A4,I4,F12.3)
618 FORMAT(/' ERROR: number of atoms > 199'/)
620 FORMAT(/' Bye...Bye....'/)
622 FORMAT(/' Input: number of atoms ',I4,
3 ' is not a multiple of 4'/)
624 FORMAT(F12.3)
632 FORMAT(/' No. of atoms is',I4,' but expected only 40'/)
END