/in/foo.cc: In function 'int main()':
/in/foo.cc:31:22: warning: unused variable 'mid' [-Wunused-variable]
    int head=1,tail=n,mid;
                      ^~~
/in/foo.cc:65:22: warning: unused variable 'mid' [-Wunused-variable]
    int head=1,tail=n,mid;
                      ^~~