How to call COBOL subprogram from main Program (Static and Dynamic)

Static Call

Main Program:

        IDENTIFICATION DIVISION.
        PROGRAM-ID. MAINPGM1
        DATA DIVISION.
        WORKING-STORAGE SECTION.
        01 B PIC X(5).
        PROCEDURE DIVISION.
            MOVE 'RAMAK' TO B.
            DISPLAY 'MAIN' B.
            CALL 'SUBPGM' USING BY REFERENCE B.
            DISPLAY 'MAIN' B.
            STOP RUN.


Sub Program:

       IDENTIFICATION DIVISION.
       PROGRAM-ID. SUBPGM.
       DATA DIVISION.
       LINKAGE SECTION.
       01 A PIC X(5).
       PROCEDURE DIVISION USING A.
           MOVE 'ROHIT' TO A.
           DISPLAY A.
           GOBACK.


Dynamic call

Main Program:

        IDENTIFICATION DIVISION.
        PROGRAM-ID. MAINPGM2.
        DATA DIVISION.
        WORKING-STORAGE SECTION.
        01 B PIC X(5).
        01 PGM PIC X(6).
        PROCEDURE DIVISION.
            MOVE 'VISHU' TO B.
            DISPLAY 'MAIN' B.
            ACCEPT PGM.
            CALL PGM USING BY REFERENCE B.
            DISPLAY 'MAIN' B.
            STOP RUN.

Sub Program:

       IDENTIFICATION DIVISION.
       PROGRAM-ID. SUBPGM.
       DATA DIVISION.
       LINKAGE SECTION.
       01 A PIC X(5).
       PROCEDURE DIVISION USING A.
           MOVE 'ROHIT' TO A.
           DISPLAY A.
           GOBACK.