/in/foo.cc: In function 'void kruskal(int, int)':
/in/foo.cc:47:48: warning: suggest parentheses around comparison in operand of '!=' [-Wparentheses]
   if (day[j][u][v]-day[i-1][u][v]!=0 || find(u)==find(v)!=0)
                                         ~~~~~~~^~~~~~~~~