/in/foo.cc: In function 'int main()':
/in/foo.cc:27:8: warning: suggest parentheses around '+' inside '>>' [-Wparentheses]
   mid=l+r>>1;
       ~^~
/in/foo.cc: In function 'void get_mu()':
/in/foo.cc:9:18: warning: iteration 999998 invokes undefined behavior [-Waggressive-loop-optimizations]
   if(!not_prime[i]) prime[++t]=i,mu[i]=-1;
       ~~~~~~~~~~~^
/in/foo.cc:8:15: note: within this loop
  for(int i=2;i<=N;i++) {
              ~^~~