foo.cc: In function 'void solve()':
foo.cc:41:7: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
  scanf("%d%d%d%d", &n, &w, &q, &opt);
  ~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
foo.cc:44:8: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
   scanf("%d", a + i);
   ~~~~~^~~~~~~~~~~~~
foo.cc:51:90: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
   scanf("%d%d%d", &l, &r, &k), l ^= opt * lastans, r ^= opt * lastans, k ^= opt * lastans, --l;
   ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~
foo.cc: In function 'int main()':
foo.cc:65:10: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result]
   freopen("input.txt", "r", stdin);
   ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~

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