/in/foo.cc: In function 'void E_prime()':
/in/foo.cc:12:19: warning: iteration 9999999 invokes undefined behavior [-Waggressive-loop-optimizations]
         if (!vis[i])
              ~~~~~^
/in/foo.cc:10:23: note: within this loop
     for (int i = 2; i <= 10000001; i++)
                     ~~^~~~~~~~~~~