foo.cc: In function 'int main()':
foo.cc:25:15: warning: variable 'n2' set but not used [-Wunused-but-set-variable]
   25 |  int k1,k2,n1,n2,y1,y2,r1,r2,sum=0;
      |               ^~
foo.cc:25:21: warning: variable 'y2' set but not used [-Wunused-but-set-variable]
   25 |  int k1,k2,n1,n2,y1,y2,r1,r2,sum=0;
      |                     ^~
foo.cc:25:27: warning: variable 'r2' set but not used [-Wunused-but-set-variable]
   25 |  int k1,k2,n1,n2,y1,y2,r1,r2,sum=0;
      |                           ^~

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