#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
const double pi=3.141592653589793;
typedef unsigned long long ull;
typedef long double ldouble;
const ll INF=1e18;
#define rep(i, n) for(int i = 0; i < (int)(n); i++)
#define rep2(i, s, n) for (int i = (s); i < (int)(n); i++)
template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return 1; } return 0; }
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return 1; } return 0; }

template<class Abel> struct UnionFind {
    vector<int> par;
    vector<int> rank;
    vector<Abel> diff_weight;

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

    void init(int n = 1, Abel SUM_UNITY = 0) {
        par.resize(n); rank.resize(n); diff_weight.resize(n);
        for (int i = 0; i < n; ++i) par[i] = i, rank[i] = 0, diff_weight[i] = SUM_UNITY;
    }

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

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

    bool issame(int x, int y) {
        return root(x) == root(y);
    }

    bool merge(int x, int 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(int x, int y) {
        return weight(y) - weight(x);
    }
};

// http://judge.u-aizu.ac.jp/onlinejudge/description.jsp?id=1330

int main(){
    int n, m, a, b, d;
    char c;
    while(cin >> n >> m){
        if(n == 0) break;
        UnionFind<int> uf(n);
        rep(i, m){
            cin >> c;
            if(c == '!'){
                cin >> a >> b >> d;
                --a;
                --b;
                uf.merge(a, b, d);
            }
            else if(c == '?'){
                cin >> a >> b;
                a--;
                b--;
                if(uf.issame(a, b)){
                    cout << uf.diff(a, b) << endl;
                }
                else {
                    puts("UNKNOWN");
                }
            }
        }
    }
}
