/in/foo.c:5:5: error: variably modified 'sum' at file scope
 int sum[maxn];
     ^~~
/in/foo.c:6:4: error: variably modified 't' at file scope
 ll t[maxn<<2],a[maxn];
    ^
/in/foo.c:6:15: error: variably modified 'a' at file scope
 ll t[maxn<<2],a[maxn];
               ^