foo.cpp: In function 'int C(int, int)':
foo.cpp:56:2: warning: this 'while' clause does not guard... [-Wmisleading-indentation]
  while(x1<=0) x1+=mod;while(x2<=0) x2+=mod;
  ^~~~~
foo.cpp:56:23: note: ...this statement, but the latter is misleadingly indented as if it is guarded by the 'while'
  while(x1<=0) x1+=mod;while(x2<=0) x2+=mod;
                       ^~~~~