foo.cc: In function 'int main()':
foo.cc:16:10: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
     scanf("%lld%lld",&n,&m); getchar();
     ~~~~~^~~~~~~~~~~~~~~~~~
foo.cc:18:36: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
         for(ll i=0; i<n; i++) scanf("%s",a[k][i]);
                               ~~~~~^~~~~~~~~~~~~~

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