/in/foo.cc: In function 'int main()':
/in/foo.cc:60:20: warning: suggest parentheses around '+' inside '>>' [-Wparentheses]
   if(check(mid = l + r >> 1)) ans = mid,r = mid - 1;
                  ~~^~~
/in/foo.cc: In function 'void pre()':
/in/foo.cc:28:12: warning: iteration 499999 invokes undefined behavior [-Waggressive-loop-optimizations]
   if(!vis[i])
       ~~~~~^
/in/foo.cc:7:45: note: within this loop
 #define rep(i,x,y) for(register ll i = x ;i <= y; ++i)
/in/foo.cc:26:6:
  rep(i,2,5000000)
      ~~~~~                                   
/in/foo.cc:26:2: note: in expansion of macro 'rep'
  rep(i,2,5000000)
  ^~~
/in/foo.cc: In function 'int main()':
/in/foo.cc:63:8: warning: 'ans' may be used uninitialized in this function [-Wmaybe-uninitialized]
  printf("%lld\n",ans);
  ~~~~~~^~~~~~~~~~~~~~