#include <bits/stdc++.h>
using namespace std;

#ifdef _WIN32
#define scanfll(x) scanf("%I64d", x)
#define printfll(x) printf("%I64d", x)
#else
#define scanfll(x) scanf("%lld", x)
#define printfll(x) printf("%lld", x)
#endif
#define rep(i,n) for(long long i = 0; i < (long long)(n); i++)
#define repi(i,a,b) for(long long i = (long long)(a); i < (long long)(b); i++)
#define pb push_back
#define all(x) (x).begin(), (x).end()
#define fi first
#define se second
#define mt make_tuple
#define mp make_pair
template<class T1, class T2> bool chmin(T1 &a, T2 b) { return b < a && (a = b, true); }
template<class T1, class T2> bool chmax(T1 &a, T2 b) { return a < b && (a = b, true); }

using ll = long long; using ld = long double; using vll = vector<ll>; using vvll = vector<vll>; using vld = vector<ld>; 
using vi = vector<int>; using vvi = vector<vi>;
vll conv(vi& v) { vll r(v.size()); rep(i, v.size()) r[i] = v[i]; return r; }
using P = pair<ll, ll>;

template <typename T, typename U> ostream &operator<<(ostream &o, const pair<T, U> &v) {  o << "(" << v.first << ", " << v.second << ")"; return o; }
template<size_t...> struct seq{}; template<size_t N, size_t... Is> struct gen_seq : gen_seq<N-1, N-1, Is...>{}; template<size_t... Is> struct gen_seq<0, Is...> : seq<Is...>{};
template<class Ch, class Tr, class Tuple, size_t... Is>
void print_tuple(basic_ostream<Ch,Tr>& os, Tuple const& t, seq<Is...>){ using s = int[]; (void)s{0, (void(os << (Is == 0? "" : ", ") << get<Is>(t)), 0)...}; }
template<class Ch, class Tr, class... Args> 
auto operator<<(basic_ostream<Ch, Tr>& os, tuple<Args...> const& t) -> basic_ostream<Ch, Tr>& { os << "("; print_tuple(os, t, gen_seq<sizeof...(Args)>()); return os << ")"; }
ostream &operator<<(ostream &o, const vvll &v) { rep(i, v.size()) { rep(j, v[i].size()) o << v[i][j] << " "; cout << endl; } return o; }
template <typename T> ostream &operator<<(ostream &o, const vector<T> &v) { o << '['; rep(i, v.size()) o << v[i] << (i != v.size()-1 ? ", " : ""); o << "]";  return o; }
template <typename T>  ostream &operator<<(ostream &o, const set<T> &m) { o << '['; for (auto it = m.begin(); it != m.end(); it++) o << *it << (next(it) != m.end() ? ", " : ""); o << "]";  return o; }
template <typename T, typename U>  ostream &operator<<(ostream &o, const map<T, U> &m) { o << '['; for (auto it = m.begin(); it != m.end(); it++) o << *it << (next(it) != m.end() ? ", " : ""); o << "]";  return o; }
template <typename T, typename U>  ostream &operator<<(ostream &o, const unordered_map<T, U> &m) { o << '['; for (auto it = m.begin(); it != m.end(); it++) o << *it; o << "]";  return o; }
void printbits(ll mask, ll n) { rep(i, n) { cout << !!(mask & (1ll << i)); } cout << endl; }
#define ldout fixed << setprecision(40) 

static const double EPS = 1e-14;
static const long long INF = 1e18;
static const long long mo = 1e9+7;

struct UnionFind {
    // ?????????????????????????????????
    // ????????????-1 * ????????¨????????????
    vector<int> data;
    
    // ????????????????????????-???
    // ?????????INF
    vector<ll> w; 

    UnionFind(int size) : data(size, -1), w(size, 0) { }
    // x, y????????????
    bool unite(int x, int y, int k) {
        ll wx = getWeight(x), wy = getWeight(y);
        x = root(x); y = root(y);
        if (x == y) 
            return 0;
        if (data[y] < data[x]) {
            swap(x, y);
            swap(wx, wy);
            k *= -1;
        }
        data[x] += data[y]; 
        data[y] = x;
//        cout << k << " " << wx << " " << wy << endl;
        w[y] = -k + wx - wy;
        return true;
    }
    // x, y?????????????????????1
    bool find(int x, int y) {
        return root(x) == root(y);
    }
    // x???????????¢??????????????????????????????????????°???
    int root(int x) {
        return data[x] < 0 ? x : root(data[x]);
//        return data[x] < 0 ? x : data[x] = root(data[x]);
    }
    ll getWeight(int x) {
        return data[x] < 0 ? 0 : w[x] + getWeight(data[x]);
    }
    // x??????????????????????????§???????????????
    int size(int x) {
        return -data[root(x)];
    }
    // ?????¢??????????????????????????°?????????
    int setNum(void) {
        map<int, int> c;
        rep(i, data.size()) {
            c[root(i)]++;
        }
        return c.size();
    }
    // O(n)
    // ???????????¨?????¨??¨???????´??????????
    vector<vector<int>> getUnionList(void) {
        map<int, vector<int>> c;
        for (int i = 0; i < data.size(); i++) 
            c[root(i)].pb(i);
        vector<vector<int>> v;
        for (auto x : c) 
            v.push_back(x.second);
        return v;
    }
    void print(void) {
        auto c = getUnionList();
        for (auto x : c) {
            for (auto y : x) 
                cout << y << " ";
            cout << endl;
        }
    }
};

int main(void) {
    cin.tie(0); ios::sync_with_stdio(false);

    ll n, m; 
    while (cin >> n >> m && n && m) {
        UnionFind uf(n);
        rep(i, m) {
            char c; cin >> c;
            if (c == '!') {
                ll x, y, w; cin >> x >> y >> w; x--; y--;
                uf.unite(x, y, w);
            } else {
                ll x, y; cin >> x >> y; x--; y--;
                if (!uf.find(x, y)) {
                    cout << "UNKNOWN" << endl;
                } else {
                    cout << uf.getWeight(x) - uf.getWeight(y) << endl;
                }
            }
            /*
            cout << uf.data << endl;
            cout << uf.w << endl;
            */
        }

    }

    return 0;
}

Measured memory_bytes: 4276