foo.cc: In function 'int main()':
foo.cc:13:22: warning: comparison of integer expressions of different signedness: 'int' and 'long long unsigned int' [-Wsign-compare]
   13 |         for(int i=0;i<len;i++)
      |                     ~^~~~
foo.cc:19:18: warning: format '%d' expects argument of type 'int', but argument 2 has type 'long long unsigned int' [-Wformat=]
   19 |         printf("%d\n",ans);
      |                 ~^    ~~~
      |                  |    |
      |                  int  long long unsigned int
      |                 %lld

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