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

enum { BASE = 10 };
int main(int argc, char *argv[]) {
    int nproc = strtol(argv[1], NULL, BASE);
    key_t key = ftok("/", 1);
    int semid = semget(key, nproc, 0666 | IPC_CREAT | IPC_EXCL);
    if (semid < 0) {
        _exit(errno);
    }
    pid_t p;
    int x;
    for (int i = 0; i < nproc; ++i) {
        if ((p = fork()) == -1) {
            _exit(errno);
        }
        if (!p) {
            while (semop(semid, (struct sembuf[]){{i, -1, 0}}, 1) >= 0) {
                if(scanf("%d", &x) != 1) {
                    semctl(semid, 0, IPC_RMID);
                    _exit(0);
                }
                printf("%d %d\n", i, x);
                fflush(stdout);
                semop(semid, (struct sembuf[]) {{x % nproc, 1, 0}}, 1);
            }
        }
    }
    if (semop(semid, (struct sembuf[]) {{0, 1, 0}}, 1) < 0) {
        _exit(errno);
    }
    for (int i = 0; i < nproc; ++i) {
        wait(NULL);
    }
}