foo.cc: In function 'int main()':
foo.cc:26:9: warning: variable 'max' set but not used [-Wunused-but-set-variable]
     int max=sum[1];
         ^~~
foo.cc:12:10: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
     scanf("%d%d",&n,&m);
     ~~~~~^~~~~~~~~~~~~~
foo.cc:14:14: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
         scanf("%d%d",&vn[i].id,&vn[i].num);
         ~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~

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