/in/foo.cc: In function 'void prime()':
/in/foo.cc:17:18: warning: iteration 9999999 invokes undefined behavior [-Waggressive-loop-optimizations]
   sum[i]+=sum[i-1]; 
                  ^
/in/foo.cc:10:15: note: within this loop
  for(int i=2;i<=10000001;i++)
              ~^~~~~~~~~~