/in/foo.cc: In function 'int main()':
/in/foo.cc:22:13: warning: unused variable 'v' [-Wunused-variable]
     for(int v,id,i=2;i<=n+1;i++){
             ^
/in/foo.cc:22:15: warning: unused variable 'id' [-Wunused-variable]
     for(int v,id,i=2;i<=n+1;i++){
               ^~