module Main where
import Control.Concurrent
import Control.Concurrent.MVar

await :: MVar Int -> MVar Int-> IO()
await mvar fim =
    do{
        var <- takeMVar mvar;
        if(var==0)
            then do
                aux <- takeMVar fim;
                putMVar fim (aux-1);
                return();
            else
                putMVar mvar var;
                await mvar fim;
}

countDown :: MVar Int -> MVar Int-> IO()
countDown mvar fim =
    do{
       var <- takeMVar mvar;
       putMVar mvar (var-1);
       aux <- takeMVar fim;
       putMVar fim (aux-1);
}

waitThread :: MVar Int -> IO()
waitThread mvar =
    do{
       fim <- takeMVar mvar;
       if(fim>0)
            then do{
                putMVar mvar fim;
                waitThread mvar;
            }
        else
            return ();
}

main :: IO()
main = do{
    fim <- newMVar 10;
    var <- newMVar 5;
    forkIO(await var fim);
    forkIO(await var fim);
    forkIO(await var fim);
    forkIO(countDown var fim);
    forkIO(countDown var fim);
    forkIO(countDown var fim);
    forkIO(await var fim);
    forkIO(countDown var fim);
    forkIO(countDown var fim);
    forkIO(await var fim);
    waitThread fim;
}