#include <bits/stdc++.h>
#include <iomanip>
#include <math.h>
#include <unistd.h>
#include <stdio.h>
#define all(a) (a).begin(),(a).end()
#define vecin(a) rep(i,a.size())cin >> a[i]
#define vecout(a) rep(i,a.size()){cout << a[i];cout << (i == a.size() - 1 ? "\n":" ");}
#define rep(i,x) for(ll i = 0;i<x;i++)
#define REP(i,x) for(ll i = 1;i<=x;i++)
#define mp make_pair
using ll = long long;
using ld = long double;
using namespace std;
using dou = double;
const ll inf = 2147483647;
const ll INF = 1LL << 60;
const dou pi = 3.14159265358;
const ll mod = 1000000007LL;
//const ll mod = 998244353LL;
typedef pair<ll,ll> P;
using graph = vector<vector<ll>>;
template<class T> inline bool chmax(T& a, T b){if(a < b){a = b; return true;}return false;}
template<class T> inline bool chmin(T& a, T b){if(a > b){a = b; return true;}return false;}
template<class T> inline bool change(T a,T b){if(a > b){swap(a,b);return true;}return false;}
template<class T>
T gcd(T a,T b){
    if(a < b)swap(a,b);
    if(a % b == 0)return b;
    else return gcd(b,a%b);
}
template<class T>
T lcm(T a,T b){
    return a / gcd(a,b) * b;
}

//素数判定O(sqrt(N))
template<class T>
inline bool isp(T n){
    bool res = true;
    if(n == 1)return false;
    else{
        for(ll i = 2;i * i <= n;i++){
            if(n % i == 0){
                res = false;
                break;
            }
        }
        return res;
    }
}
const ll cmax = 1000000;
ll fac[cmax], finv[cmax], inv[cmax];

// テーブルを作る前処理
void COMinit() {
    fac[0] = fac[1] = 1;
    finv[0] = finv[1] = 1;
    inv[1] = 1;
    for (ll i = 2; i < cmax; i++){
        fac[i] = fac[i - 1] * i % mod;
        inv[i] = mod - inv[mod%i] * (mod / i) % mod;
        finv[i] = finv[i - 1] * inv[i] % mod;
    }
}

// 二項係数計算
ll nCk(ll n, ll k){
    if (n < k) return 0;
    if (n < 0 || k < 0) return 0;
    return fac[n] * (finv[k] * finv[n - k] % mod) % mod;
}
//nのm乗をMODで割ったあまりO(logm)
ll modpow(ll n,ll m,ll MOD){
    if(m == 0)return 1;
    if(m < 0)return -1;
    ll res = 1;
    while(m){
        if(m & 1)res = (res * n) % MOD;
        m >>= 1;
        n *= n;
        n %= MOD;
    }
    return res;
}
ll mypow(ll n,ll m){
    if(m == 0)return 1;
    if(m < 0)return -1;
    ll res = 1;
    while(m){
        if(m & 1)res = (res * n);
        m >>= 1;
        n *= n;
    }
    return res;
}

template<class Abel,class T>//重さの型,それ以外の型(メモリあるならllでOK)
struct UnionFind {
    vector<T> par;
    vector<T> rank;
    vector<Abel> diff_weight;

    UnionFind(T n = 1,Abel SUM_UNITY = 0){
        init(n, SUM_UNITY);
    }

    void init(T n = 1,Abel SUM_UNITY = 0){
        par.resize(n); rank.resize(n); diff_weight.resize(n);
        rep(i,n){
            par[i] = i, rank[i] = 0, diff_weight[i] = SUM_UNITY;
        }
    }

    T root(T x) {
        if (par[x] == x) {
            return x;
        }
        else {
            T r = root(par[x]);
            diff_weight[x] += diff_weight[par[x]];
            return par[x] = r;
        }
    }

    Abel weight(T x) {
        root(x);
        return diff_weight[x];
    }

    bool same(T x, T y) {
        return root(x) == root(y);
    }

    bool unite(T x,T y,Abel w) {
        w += weight(x); w -= weight(y);
        x = root(x); y = root(y);
        if (x == y) return false;
        if (rank[x] < rank[y]) swap(x, y), w = -w;
        if (rank[x] == rank[y]) ++rank[x];
        par[y] = x;
        diff_weight[y] = w;
        return true;
    }

    Abel diff(T x,T y) {
        return weight(y) - weight(x);
    }
};

ll N,M;
void solve(ll N,ll M){
    UnionFind<ll,ll> UF(N);
    char tipe;
    rep(i,M){
        cin >> tipe;
        if(tipe == '!'){
            ll a,b,c;
            cin >> a >> b >> c;
            a--;b--;
            UF.unite(a,b,c);
        }
        else{
            ll a,b;
            cin >> a >> b;
            a--;b--;
            if(!UF.same(a,b)){
                cout << "UNKNOWN\n";
            }
            else{
                cout << UF.diff(a,b) << "\n";
            }
        }
    }
}
int main(){
    ios::sync_with_stdio(false);
    cin.tie(0);cout.tie(0);
    while(1){
        cin >> N >> M;
        if(N == 0 && M == 0)break;
        solve(N,M);
    }
}


Measured memory_bytes: 5136