#include <stdio.h>
    #include <stdlib.h>
    #include <errno.h>
    #include <sys/types.h>
    #include <sys/ipc.h>
    #include <sys/sem.h>

    int main(void)
    {
        key_t key1;
        int semid1;


static struct sembuf Decr = {0,-1,SEM_UNDO};
static struct sembuf Incr = {0,1,SEM_UNDO};


	key1 = ftok("reader.c", 'X');
	semid1= semget(key1,2,IPC_CREAT | 0600);
	semctl(semid1,0,SETVAL,1);
	semctl(semid1,1,SETVAL,1);


int i;
for(i = 0; i<5; i++){

semctl(semid1,0,SETVAL,0);
semop(semid1,&Decr,1);
printf("read\n");
sleep(2);
printf("done\n");
semctl(semid1,0,SETVAL,1);
semop(semid1,&Incr,1);
sleep(4);

}


        return 0;
    }