foo.cc: In function 'int main()':
foo.cc:5:9: warning: unused variable 'j' [-Wunused-variable]
    5 |  int i, j, k, a, b, c, d;
      |         ^
foo.cc:5:12: warning: unused variable 'k' [-Wunused-variable]
    5 |  int i, j, k, a, b, c, d;
      |            ^
foo.cc:6:21: warning: unused variable 'num' [-Wunused-variable]
    6 |  long long sum = 0, num;
      |                     ^~~

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