#include <stdlib.h>
#include <stdio.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <unistd.h>
#include <errno.h>
#include <signal.h>

volatile sig_atomic_t flag = 0;
int targetpid;
int max;

void handler(int signal) {
    flag = 1;
}

void proc(FILE *fr, FILE *fw, int curr)
{
    int x;
    while (1) {
        while (!flag) {
            pause();
        }
        flag = 0;
        fscanf(fr, "%d", &x);
        if (x >= max) {
            break;
        }
        printf("%d %d\n", curr, x);
        fflush(stdout);
        x++;
        fprintf(fw, "%d\n", x);
        kill(targetpid, SIGUSR1);
        fflush(fw);
    }
    fclose(fr);
    fclose(fw);
}

int main(int argc, char *argv[]) {

    max = strtol(argv[1], NULL, 10);
    int fd[2];
    pipe(fd);
    FILE *fr = fdopen(fd[0], "r");
    FILE *fw = fdopen(fd[1], "w");

    struct sigaction action =
    {
        .sa_handler = handler,
        .sa_flags = SA_RESTART
    };
    sigaction(SIGUSR1, &action, NULL);
    int pid1;
    int pid2;

    if (!(pid1 = fork())) {
        while (!flag) {
            pause();
        }
        fscanf(fr, "%d", &targetpid);

        proc(fr, fw, 1);
        close(fd[0]);
        close(fd[1]);
        exit(0);
    }

    if (!(pid2 = fork())) {
        while (!flag) {
            pause();
        }
        flag = 0;

        fscanf(fr, "%d", &targetpid);
        fprintf(fw, "%d\n", getpid());
        fflush(fw);
        fprintf(fw, "%d\n", 1);
        fflush(fw);
        kill(targetpid, SIGUSR1);

        proc(fr, fw, 2);
        close(fd[0]);
        close(fd[1]);
        exit(0);
    }

    fprintf(fw, "%d\n", pid1);
    fflush(fw);
    fclose(fr);
    fclose(fw);
    close(fd[1]);
    close(fd[0]);
    kill(pid2, SIGUSR1);

    int finish = wait(NULL);
    if (finish == pid1) {
        kill(pid2, SIGKILL);
    } else {
        kill(pid1, SIGKILL);
    }
    wait(NULL);
    printf("Done\n");
    fflush(stdout);
    exit(0);
}