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

volatile sig_atomic_t cnt;
volatile sig_atomic_t must_exit = 0;

void handle_sigterm(int signum)
{
    must_exit = 1;
}

void handle_sigusr1(int signum)
{
    cnt += 1;
    printf("%d\n", cnt);
    fflush(stdout);
}

void handle_sigusr2(int signum)
{
    cnt *= -1;
    printf("%d\n", cnt);
    fflush(stdout);
}

int main()
{
    struct sigaction action_usr1;
    memset(&action_usr1, 0, sizeof(action_usr1));
    action_usr1.sa_handler = handle_sigusr1;
    action_usr1.sa_flags = SA_RESTART;
    sigaction(SIGUSR1, &action_usr1, NULL);

    struct sigaction action_usr2;
    memset(&action_usr2, 0, sizeof(action_usr2));
    action_usr2.sa_handler = handle_sigusr2;
    action_usr2.sa_flags = SA_RESTART;
    sigaction(SIGUSR2, &action_usr2, NULL);

    struct sigaction action_term;
    memset(&action_term, 0, sizeof(action_term));
    action_term.sa_handler = handle_sigterm;
    action_term.sa_flags = SA_RESTART;
    sigaction(SIGTERM, &action_term, NULL);

    printf("%d\n", getpid());
    fflush(stdout);

    scanf("%d", &cnt);

    while (!must_exit) {
        pause();
    }
    return 0;
}