/in/foo.cc: In function 'void dfs1(long long int, long long int)':
/in/foo.cc:6:36: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
 #define F(i, j, k) for(ll i = j; i <= k; ++i)
                                     
/in/foo.cc:28:7:
     F(i, 0, to[x].size()-1) {
       ~~~~~~~~~~~~~~~~~~~~          
/in/foo.cc:28:5: note: in expansion of macro 'F'
     F(i, 0, to[x].size()-1) {
     ^
/in/foo.cc: In function 'bool dfs2(long long int, long long int, long long int)':
/in/foo.cc:6:36: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
 #define F(i, j, k) for(ll i = j; i <= k; ++i)
                                     
/in/foo.cc:45:7:
     F(i, 0, to[x].size() - 1) {
       ~~~~~~~~~~~~~~~~~~~~~~        
/in/foo.cc:45:5: note: in expansion of macro 'F'
     F(i, 0, to[x].size() - 1) {
     ^