/in/foo.cc: In function 'int main()':
/in/foo.cc:26:14: warning: unused variable '_' [-Wunused-variable]
  for(int i=1,_=scanf("%d %d %d",&d,&n,&m);i<=n;scanf("%d",&t[i]),a[i]=t[i]-t[i-1],ma=a[i]>ma?a[i]:ma,a[n+1]=i==n?d-t[n]:0,i++);
              ^