foo.cc: In function 'int main()':
foo.cc:6:12: warning: unused variable 'j' [-Wunused-variable]
  int n,m,i,j,s,tot=0;
            ^
foo.cc:6:14: warning: unused variable 's' [-Wunused-variable]
  int n,m,i,j,s,tot=0;
              ^
foo.cc:7:7: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
  scanf("%d%d",&n,&m);
  ~~~~~^~~~~~~~~~~~~~
foo.cc:10:8: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
   scanf("%d",&a[i]);
   ~~~~~^~~~~~~~~~~~

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