foo.cc: In function 'int main()':
foo.cc:44:12: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result]
     freopen("P1135_4.in", "r", stdin);
     ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~
foo.cc:45:10: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
     scanf("%d%d%d", &n, &a, &b);
     ~~~~~^~~~~~~~~~~~~~~~~~~~~~
foo.cc:46:39: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
     for (int i = 1; i <= n; i++) scanf("%d", &k[i]);
                                  ~~~~~^~~~~~~~~~~~~

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