foo.cc: In function 'void solve(int, int, int, int)':
foo.cc:9:12: warning: unused variable 'k' [-Wunused-variable]
    9 |  int i, j, k;
      |            ^
foo.cc: In function 'int main()':
foo.cc:28:12: warning: unused variable 'k' [-Wunused-variable]
   28 |  int i, j, k;
      |            ^

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