foo.cc: In function 'void Clear(int)':
foo.cc:90:9: warning: unused variable 'i2' [-Wunused-variable]
   90 |    int &i2=son[i][j-1];
      |         ^~
foo.cc: In function 'int main()':
foo.cc:113:10: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
  113 |     scanf("%d %d",&n,&m);
      |     ~~~~~^~~~~~~~~~~~~~~
foo.cc:117:11: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
  117 |      scanf("%d %d",&x,&y);
      |      ~~~~~^~~~~~~~~~~~~~~
foo.cc:123:11: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
  123 |      scanf("%d %d",&x,&y);
      |      ~~~~~^~~~~~~~~~~~~~~

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