foo.cc: In function 'int main()':
foo.cc:9:7: warning: suggest explicit braces to avoid ambiguous 'else' [-Wdangling-else]
     if(n==2)//1 2
       ^
foo.cc:18:4: warning: suggest explicit braces to avoid ambiguous 'else' [-Wdangling-else]
  if(n==3)//1 2 4
    ^
foo.cc:56:4: warning: suggest explicit braces to avoid ambiguous 'else' [-Wdangling-else]
  if(n==5)
    ^

自豪的采用HydroJudge(https://github.com/hydro-dev/Hydro)进行评测。