#![allow(non_snake_case, unused_imports)]
//////////////////////////////// LIBRARY START ////////////////////////////////
#[macro_use]
pub mod contest {
    #[macro_use]
    pub mod prelude {
        pub use self::myvec::*;
        #[macro_use]
        pub mod primitive {
            pub trait ToUsize: Sized {
                fn to_usize(self) -> usize;
            }

            impl ToUsize for i32 {
                #[inline]
                fn to_usize(self) -> usize {
                    self as usize
                }
            }

            impl ToUsize for i64 {
                #[inline]
                fn to_usize(self) -> usize {
                    self as usize
                }
            }

            impl ToUsize for usize {
                #[inline]
                fn to_usize(self) -> usize {
                    self
                }
            }
        }
        #[macro_use]
        pub mod myvec {
            use std::fmt;
            use std::iter::FromIterator;
            use std::ops::*;

            pub use super::primitive::ToUsize;

            /// `Vec` indexable with `i32`, `i64` or `usize`.
            #[derive(Clone, Debug, PartialEq, PartialOrd)]
            pub struct MyVec<T>(pub Vec<T>);

            /// Creates `MyVec`
            #[macro_export]
            macro_rules! v {
    ( $( $x:expr ),* ) => {
        MyVec(vec![ $( $x, )* ])
    };
    ( $x:expr ; $n:expr ) => {
        {
            MyVec(vec![$x; $n as usize])
        }
    };
}

            impl<T: fmt::Display> fmt::Display for MyVec<T> {
                fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
                    let n = self.len();
                    for i in 0..n {
                        let r = if i < n - 1 {
                            writeln!(f, "{}", self.0[i])
                        } else {
                            write!(f, "{}", self.0[i])
                        };
                        if r.is_err() {
                            return r;
                        }
                    }
                    Ok(())
                }
            }

            impl<T> Deref for MyVec<T> {
                type Target = Vec<T>;

                #[inline]
                fn deref(&self) -> &Vec<T> {
                    &self.0
                }
            }

            impl<T> DerefMut for MyVec<T> {
                #[inline]
                fn deref_mut(&mut self) -> &mut Vec<T> {
                    &mut self.0
                }
            }

            impl<T> FromIterator<T> for MyVec<T> {
                #[inline]
                fn from_iter<I: IntoIterator<Item = T>>(iter: I) -> Self {
                    MyVec(Vec::from_iter(iter))
                }
            }

            impl<T, I: ToUsize> Index<I> for MyVec<T> {
                type Output = T;

                #[inline]
                fn index(&self, i: I) -> &T {
                    &self.0[i.to_usize()]
                }
            }

            impl<T, I: ToUsize> IndexMut<I> for MyVec<T> {
                #[inline]
                fn index_mut(&mut self, i: I) -> &mut T {
                    &mut self.0[i.to_usize()]
                }
            }

            #[test]
            fn test_myvec() {
                let mut x = v![3, 2, 1];
                x.sort();
                assert_eq!(vec![1, 2, 3], *x);
                let i = 1i32;
                assert_eq!(2, x[i]);
                x[i] = 3;
                assert_eq!(3, x[i]);
                let u = 1usize;
                assert_eq!(3, x[u]);
                x[u] = 2;
                assert_eq!(2, x[u]);
                assert_eq!(2, x[1]);

                assert_eq!("MyVec([1, 2, 3])", format!("{:?}", x));
                assert_eq!(v![1, 2, 3], x);

                assert_eq!("1\n2\n3", format!("{}", x));

                let mut y = v![v![1, 2]; 3];
                y[0][0] = 2;
                assert_eq!(vec![2, 2], *y[0]);
                assert_eq!(vec![1, 2], *y[1]);
            }
        }
    }
    #[macro_use]
    pub mod io {
        /// Scanner
        ///
        /// # Example
        /// ```
        /// use contest::io::Scanner;
        /// let mut sc = Scanner::new("1 2 \n\n \r\t \n 3".as_bytes());
        /// assert_eq!("1".to_string(), sc.next::<String>());
        /// let v = sc.nexts(2);
        /// assert_eq!(2i32, v[0]);
        /// assert_eq!(3i32, v[1]);
        ///
        /// // To create a scanner from stdin:
        /// Scanner::new(std::io::stdin());
        /// ```
        use std;
        use std::io;
        use std::io::BufRead;

        use super::prelude::MyVec;

        pub struct Scanner<R: io::Read> {
            br: io::BufReader<R>,
            // Read tokens are stored in reversed order per line.
            buf: Vec<String>,
        }

        pub fn new<R: io::Read>(r: R) -> Scanner<R> {
            Scanner::new(r)
        }

        impl<R: io::Read> Scanner<R> {
            #[inline]
            pub fn new(r: R) -> Scanner<R> {
                Scanner {
                    br: io::BufReader::new(r),
                    buf: vec![],
                }
            }
            #[inline]
            pub fn next<T>(&mut self) -> T
            where
                T: std::str::FromStr,
                T::Err: std::fmt::Debug,
            {
                self.next_string()
                    .map(|s| s.parse::<T>().expect("Parse failed: "))
                    .expect("Unexpected EOF")
            }
            #[inline]
            pub fn nexts<T>(&mut self, n: i32) -> MyVec<T>
            where
                T: std::str::FromStr,
                T::Err: std::fmt::Debug,
            {
                let mut res = v![];
                for _ in 0..n {
                    res.push(self.next());
                }
                res
            }
            fn next_string(&mut self) -> Option<String> {
                self.buf.pop().or_else(|| match self.update() {
                    true => self.next_string(),
                    false => None,
                })
            }
            #[inline]
            fn update(&mut self) -> bool {
                let mut s = String::new();
                let res = self.br.read_line(&mut s);
                match res.expect("I/O error.") {
                    0 => false,
                    _ => {
                        self.buf = s.split_whitespace().map(|x| x.to_string()).rev().collect();
                        true
                    }
                }
            }
        }

        #[test]
        fn test_next() {
            let mut sc = new("hoge".as_bytes());
            let s: String = sc.next();
            assert_eq!("hoge", s);
        }
    }
}
//////////////////////////////// LIBRARY END ////////////////////////////////

use contest::io::Scanner;
use contest::prelude::MyVec;

const INF: i32 = 1_000_000_000;
fn main() {
    let mut sc = Scanner::new(std::io::stdin());

    let n = sc.next::<i32>();
    let s = sc.next::<String>();

    let mut graph = v![v![]; n];
    for i in 0..(n - 1) {
        let a = sc.next::<i32>() - 1;
        let b = sc.next::<i32>() - 1;
        graph[a].push(b);
        graph[b].push(a);
    }
    let mut have = v![];
    for c in s.chars() {
        have.push(c == '1');
    }

    let mut res = INF;
    for i in 0..n {
        let (min, max, _) = dfs(&graph, &have, i, -1);
        if min == 0 {
            if res > max / 2 {
                res = max / 2;
            }
        }
    }

    println!("{}", if res == INF { -1 } else { res });
}

fn dfs(graph: &MyVec<MyVec<i32>>, have: &MyVec<bool>, root: i32, parent: i32) -> (i32, i32, i32) {
    // min, max, num
    let mut tot = 0;
    let mut res_min = 0;
    let mut res_max = 0;
    for j in &*graph[root] {
        if *j == parent {
            continue;
        }
        let tup = dfs(graph, have, *j, root);
        let mut min = tup.0;
        let mut max = tup.1;
        let num = tup.2;
        tot += num;
        min += num;
        max += num;

        if max < res_min {
            res_min = res_min - max;
        } else if res_max < min {
            res_min = min - res_max;
        } else {
            if ((res_min + min) & 1) == 0 {
                res_min = 0;
            } else {
                res_min = 1;
            }
        }
        res_max += max;
    }
    if have[root] {
        tot += 1;
    }
    (res_min, res_max, tot)
}


Measured memory_bytes: 4604