/in/foo.cc: In function 'int main()':
/in/foo.cc:27:12: warning: unused variable 'len1' [-Wunused-variable]
  int n,i,j,len1,len2,len,sum=0,k;
            ^~~~
/in/foo.cc:27:17: warning: unused variable 'len2' [-Wunused-variable]
  int n,i,j,len1,len2,len,sum=0,k;
                 ^~~~
/in/foo.cc:27:22: warning: unused variable 'len' [-Wunused-variable]
  int n,i,j,len1,len2,len,sum=0,k;
                      ^~~