#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/wait.h>
#include <signal.h>
#include <sys/ipc.h>
#include <sys/sem.h>
#include <sys/shm.h>
#include <sys/msg.h>
#include <sys/types.h>

enum { BASE = 10 };


int main(int argc, char *argv[]) {
    setbuf(stdin, NULL);
    //int count = (int) strtol(argv[1], NULL, BASE);
    int count = 3;
    int sem_id = semget(IPC_PRIVATE, count + 1, 0666 | IPC_CREAT | IPC_EXCL);
    if (sem_id < 0) {
        exit(1);
    }
    pid_t pid[count];
    for (int i = 0; i < count; i++) {
        pid[i] = fork();
        if (pid[i] == 0) {
            while (1) {
                if ((semop(sem_id, (struct sembuf[]){{count, -1, IPC_NOWAIT}}, 1) >= 0) || (semop(sem_id, (struct sembuf[]){{i, -1, 0}}, 1) >= 0)) {
                    if (semop(sem_id, (struct sembuf[]){{i, -1, 0}}, 1) >= 0) {
                        int tmp;
                        if (scanf("%d", &tmp) == EOF) {
                            semop(sem_id,(struct sembuf[]){{count, count, 0}},1);
                        }
                        printf("%d %d\n", i, tmp);
                        tmp = ((tmp % count) + count) % count;
                        semop(sem_id,(struct sembuf[]){{tmp, 2, 0}},1);
                    } else {
                        exit(0);
                    }
                }
                /*if (semop(sem_id, (struct sembuf[]){{count, -1, 0}}, 1) >= 0) {
                    exit(0);
                }*/
            }


            /*while (semop(sem_id, (struct sembuf[]){{i, -1, 0}}, 1) >= 0) {
                int tmp;
                if (scanf("%d", &tmp) == EOF) {
                    semop(sem_id,(struct sembuf[]){{count, 1, 0}},1);
                }
                printf("%d %d\n", i, tmp);
                tmp = ((tmp % count) + count) % count;
                semop(sem_id,(struct sembuf[]){{tmp, 1, 0}},1);

            } */

        } else if (pid[i] < 0) {
            exit(1);
        }

    }
    semop(sem_id, (struct sembuf[]) {{0, 2, 0}}, 1);
    while (wait(NULL) > 0) {

    }
    semctl(sem_id, 0, IPC_RMID);
    return 0;
}