foo.cc: In function 'int main()':
foo.cc:16:6: warning: suggest explicit braces to avoid ambiguous 'else' [-Wdangling-else]
    if(a[j])
      ^
foo.cc:10:29: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
  for(int i=1;i<=n;i++) scanf("%lld",&s[i]);
                        ~~~~~^~~~~~~~~~~~~~

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