foo.c: In function 'main':
foo.c:5:20: warning: unused variable 'x' [-Wunused-variable]
     long n, s = 0, x;
                    ^
foo.c:7:2: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result]
  scanf("%ld", &n);
  ^~~~~~~~~~~~~~~~

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