/+ dub.sdl:
    name "A"
    dependency "dcomp" version=">=0.4.0"
+/

import std.stdio, std.algorithm, std.conv, std.range;
import std.typecons;

// import dcomp.scanner, dcomp.container.deque;

int main() {
    auto sc = new Scanner(stdin);
    alias E = Tuple!(int, "to");
    int n;
    sc.read(n);
    E[][] g = new E[][2*n-1];
    foreach (i; 0..n-1) {
        int a, b;
        sc.read(a, b); a--; b--;
        g[a] ~= E(n+i);
        g[n+i] ~= E(a);
        g[b] ~= E(n+i);
        g[n+i] ~= E(b);
    }
    string s;
    sc.read(s);

    n = 2*n-1;
    int[2] searchMid() {
        int[] rt = new int[n];
        int[2] lng;
        void dfs(int p, int b, int dps = 0) {
            rt[p] = b;
            if (lng[1] < dps) {
                lng = [p, dps];
            }
            foreach (e; g[p]) {
                int d = e.to;
                if (d == b) continue;
                dfs(d, p, dps+1);
            }
        }
        lng = [-1, -1];
        dfs(0, -1);
        int v = lng[0];
        lng = [-1, -1];
        dfs(v, -1);
        int[] path;
        int u = lng[0];
        while (u != v) {
            path ~= u;
            u = rt[u];
        }
        path ~= v;
//        writeln(path);
        return [path[path.length/2], path.length.to!int/2];
    }

    int[2] mid = searchMid();
//    writeln(mid);

    bool[] bc = new bool[n];
    bool[] bsm = new bool[n];
    int[] md = new int[n];
    void dfs(int p, int b) {
        if (p < (n+1)/2 && s[p] == '1') bc[p] = true;
        bsm[p] = bc[p];
        md[p] = 0;
        foreach (e; g[p]) {
            int d = e.to;
            if (d == b) continue;
            dfs(d, p);
            bsm[p] |= bsm[d];
            md[p] = max(md[p], md[d]+1);
        }
    }
    dfs(mid[0], -1);
/*    writeln(bc);
    writeln(bsm);
    writeln(md);*/
    long ans = 0;
    int calc(int p, int b) {
        int mi = 10^^9;
        foreach (e; g[p]) {
            int d = e.to;
            if (d == b) continue;
            mi = min(mi, 1+calc(d, p));
        }

        int di = md[p];
        if (bc[p]) {
            ans += di/2+1;
            return di;
        } else {
            if (mi < 10^^8) {
                ans += (di-mi)/2+1;
                return di;
            }
            return mi;
        }
    }
    calc(mid[0], -1);
    writeln(ans);

    return 0;
}
/* IMPORT /home/yosupo/Program/dcomp/source/dcomp/container/deque.d */
// module dcomp.container.deque;

struct Deque(T) {
    import core.exception : RangeError;
    import core.memory : GC;
    import std.range : ElementType, isInputRange;
    import std.traits : isImplicitlyConvertible;

    struct Payload {
        T *d;
        size_t st, length, cap;
        @property bool empty() const { return length == 0; }
        alias opDollar = length;
        ref inout(T) opIndex(size_t i) inout {
            version(assert) if (length <= i) throw new RangeError();
            return d[(st+i >= cap) ? (st+i-cap) : st+i];
        }
        private void expand() {
            import std.algorithm : max;
            assert(length == cap);
            auto nc = max(4L, 2*cap);
            T* nd = cast(T*)GC.malloc(nc * T.sizeof);
            foreach (i; 0..length) {
                nd[i] = this[i];
            }
            d = nd; st = 0; cap = nc;
        }
        void insertFront(T v) {
            if (length == cap) expand();
            if (st == 0) st += cap;
            st--; length++;
            this[0] = v; 
        }
        void insertBack(T v) {
            if (length == cap) expand();
            length++;
            this[length-1] = v; 
        }
        void removeFront() {
            assert(!empty, "Deque.removeFront: Deque is empty");        
            st++; length--;
            if (st == cap) st = 0;
        }
        void removeBack() {
            assert(!empty, "Deque.removeBack: Deque is empty");        
            length--;
        }        
    }
    struct RangeT(A) {
        alias T = typeof(*(A.p));
        alias E = typeof(A.p.d[0]);
        T *p;
        size_t a, b;
        @property bool empty() const { return b <= a; }
        @property size_t length() const { return b-a; }
        @property RangeT save() { return RangeT(p, a, b); }
        @property RangeT!(const A) save() const {
            return typeof(return)(p, a, b);
        }
        alias opDollar = length;
        @property ref inout(E) front() inout { return (*p)[a]; }
        @property ref inout(E) back() inout { return (*p)[b-1]; }
        void popFront() {
            version(assert) if (empty) throw new RangeError();
            a++;
        }
        void popBack() {
            version(assert) if (empty) throw new RangeError();
            b--;
        }
        ref inout(E) opIndex(size_t i) inout { return (*p)[i]; }
        RangeT opSlice() { return this.save; }
        RangeT opSlice(size_t i, size_t j) {
            version(assert) if (i > j || a + j > b) throw new RangeError();
            return typeof(return)(p, a+i, a+j);
        }
        RangeT!(const A) opSlice() const { return this.save; }
        RangeT!(const A) opSlice(size_t i, size_t j) const {
            version(assert) if (i > j || a + j > b) throw new RangeError();
            return typeof(return)(p, a+i, a+j);
        }
    }
    
    alias Range = RangeT!Deque;
    alias ConstRange = RangeT!(const Deque);
    alias ImmutableRange = RangeT!(immutable Deque);

    Payload *p;
    private void I() { if (!p) p = new Payload(); }
    private void C() const { assert(p, "this deque is not init"); }
    //some value
    this(U)(U[] values...) if (isImplicitlyConvertible!(U, T)) {I;
        p = new Payload();
        foreach (v; values) {
            insertBack(v);
        }
    }
    //range
    this(Range)(Range r)
    if (isInputRange!Range &&
    isImplicitlyConvertible!(ElementType!Range, T) &&
    !is(Range == T[])) {I;
        p = new Payload();
        foreach (v; r) {
            insertBack(v);
        }
    }
    
    @property bool empty() const { return (!p || p.empty); }
    @property size_t length() const { return (p ? p.length : 0); }
    alias opDollar = length;
    ref inout(T) opIndex(size_t i) inout {C; return (*p)[i]; }
    ref inout(T) front() inout {C; return (*p)[0]; }
    ref inout(T) back() inout {C; return (*p)[$-1]; }
    void insertFront(T v) {I; p.insertFront(v); }
    void insertBack(T v) {I; p.insertBack(v); }
    void removeFront() {C; p.removeFront(); }
    void removeBack() {C; p.removeBack(); }
    Range opSlice() {I; return Range(p, 0, length); }
}

unittest {
    import std.algorithm : equal;
    import std.range.primitives : isRandomAccessRange;
    import std.container.util : make;
    auto q = make!(Deque!int);
    assert(isRandomAccessRange!(typeof(q[])));

    //insert,remove
    assert(equal(q[], new int[](0)));
    q.insertBack(1);
    assert(equal(q[], [1]));
    q.insertBack(2);
    assert(equal(q[], [1, 2]));
    q.insertFront(3);
    assert(equal(q[], [3, 1, 2]) && q.front == 3);
    q.removeFront;
    assert(equal(q[], [1, 2]) && q.length == 2);
    q.insertBack(4);
    assert(equal(q[], [1, 2, 4]) && q.front == 1 && q.back == 4 && q[$-1] == 4);
    q.insertFront(5);
    assert(equal(q[], [5, 1, 2, 4]));

    //range
    assert(equal(q[][1..3], [1, 2]));
    assert(equal(q[][][][], q[]));
    //const range
    const auto rng = q[];
    assert(rng.front == 5 && rng.back == 4);
    
    //reference type
    auto q2 = q;
    q2.insertBack(6);
    q2.insertFront(7);
    assert(equal(q[], q2[]) && q.length == q2.length);

    //construct with make
    auto a = make!(Deque!int)(1, 2, 3);
    auto b = make!(Deque!int)([1, 2, 3]);
    assert(equal(a[], b[]));
}

unittest {
    Deque!int a;
    Deque!int b;
    a.insertFront(2);
    assert(b.length == 0);
}

unittest {
    import std.algorithm : equal;
    import std.range : iota;
    Deque!int a;
    foreach (i; 0..100) {
        a.insertBack(i);
    }
    assert(equal(a[], iota(100)));
}
/* IMPORT /home/yosupo/Program/dcomp/source/dcomp/scanner.d */
// module dcomp.scanner;

class Scanner {
    import std.stdio : File;
    import std.conv : to;
    import std.range : front, popFront, array, ElementType;
    import std.array : split;
    import std.traits : isSomeChar, isStaticArray, isArray; 
    import std.algorithm : map;
    File f;
    this(File f) {
        this.f = f;
    }
    string[] buf;
    private bool succ() {
        while (!buf.length) {
            if (f.eof) return false;
            buf = f.readln.split;
        }
        return true;
    }
    private bool readSingle(T)(ref T x) {
        if (!succ()) return false;
        static if (isArray!T) {
            alias E = ElementType!T;
            static if (isSomeChar!E) {
                //string or char[10] etc
                x = buf.front;
                buf.popFront;
            } else {
                static if (isStaticArray!T) {
                    //static
                    assert(buf.length == T.length);
                }
                x = buf.map!(to!E).array;
                buf.length = 0;                
            }
        } else {
            x = buf.front.to!T;
            buf.popFront;            
        }
        return true;
    }
    int read(T, Args...)(ref T x, auto ref Args args) {
        if (!readSingle(x)) return 0;
        static if (args.length == 0) {
            return 1;
        } else {
            return 1 + read(args);
        }
    }
}

unittest {
    import std.path : buildPath;
    import std.file : tempDir;
    import std.algorithm : equal;
    import std.stdio : File;
    string fileName = buildPath(tempDir, "kyuridenanmaida.txt");
    auto fout = File(fileName, "w");
    fout.writeln("1 2 3");
    fout.writeln("ab cde");
    fout.writeln("1.0 1.0 2.0");
    fout.close;
    Scanner sc = new Scanner(File(fileName, "r"));
    int a;
    int[2] b;
    char[2] c;
    string d;
    double e;
    double[] f;
    sc.read(a, b, c, d, e, f);
    assert(a == 1);
    assert(equal(b[], [2, 3]));
    assert(equal(c[], "ab"));
    assert(equal(d, "cde"));
    assert(e == 1.0);
    assert(equal(f, [1.0, 2.0]));
}
