sem_t m1=1, m2=1, sync=0, syncMul=0;
int n=0, s=0, mean=0, meanBlock=0;


int sum(int x){
  int ret;  

  P(m1);
  if(meanBlock){
    s=x;
    V(syncMul);
    ret = mean;
    P(sync);
    V(m1);
    return ret;
  }else{
    s += x;
    n++;
    V(m1);
    P(sync);
    ret = mean;
    P(m2)
    n--;
    if(n==0) V(m1);
    V(m2);
    return ret;
  }
}


void mul(int m){
  int c;

  P(m1);
  if(n>0){
    mean = s*m;
    for (c=0; c<n;c++){
      V(sync);
    }
  }else{
    meanBlock+=1;
    V(m1);
    P(syncMul);
    mean = s*m;
    V(sync);
  }
}