#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <cmath>
#include <climits>
#include <cfloat>
#include <ctime>
#include <cassert>
#include <map>
#include <utility>
#include <set>
#include <iostream>
#include <memory>
#include <string>
#include <vector>
#include <algorithm>
#include <functional>
#include <sstream>
#include <complex>
#include <stack>
#include <queue>
#include <numeric>
#include <list>
#include <iomanip>
#include <fstream>
#include <bitset>
   
using namespace std;
   
 
#define rep(i, n) for (int i = 0; i < (int)(n); ++i)
#define foreach(it, c) for (__typeof__((c).begin()) it=(c).begin(); it != (c).end(); ++it)
#define rforeach(it, c) for (__typeof__((c).rbegin()) it=(c).rbegin(); it != (c).rend(); ++it)
#define all(c) (c).begin(), (c).end()
#define rall(c) (c).rbegin(), (c).rend()
#define CL(arr, val) memset(arr, val, sizeof(arr))
#define COPY(dest, src) memcpy(dest, src, sizeof(dest))
#define ten(n) ((long long)(1e##n))
#define bin(n) (1LL << (n))
#define erep(i, n) for (int i = 0; i <= (int)(n); ++i)
#define revrep(i, n) for (int i = (n); i >= 0; --i)
#define pb push_back

template <class T> void chmax(T& a, const T& b) { a = max(a, b); }
template <class T> void chmin(T& a, const T& b) { a = min(a, b); }
 
template <class T> void uniq(vector<T>& c) { sort(c.begin(), c.end()); c.erase(unique(c.begin(), c.end()), c.end()); }
 
template <class T> string to_s(const T& a) { ostringstream os; os << a; return os.str(); }
template <class T> T to_T(const string& s) { istringstream is(s); T res; is >> res; return res; }
  
template <class T, class U> ostream& operator<<(ostream& os, pair<T, U>& p) { os << "( " << p.first << ", " << p.second << " )"; return os; }
  
template <class T> void print(T a, int n, const string& deli = " ", int br = 1) { for (int i = 0; i < n; ++i) { cout << a[i]; if (i + 1 != n) cout << deli; } while (br--) cout << endl; }
template <class T> void print(const T& c, const string& deli = " ", int br = 1) { foreach (it, c) { cout << *it; if (++it != c.end()) cout << deli;--it; } while (br--) cout << endl; }
template <class T> void print2d(T a, int w, int h, int width = -1, int br = 1) { for (int i = 0; i < h; ++i) { for (int j = 0; j < w; ++j) {    if (width != -1) cout.width(width); cout << a[i][j] << ' '; } cout << endl; } while (br--) cout << endl; }
   
template <class T> void input(T& a, int n) { for (int i = 0; i < n; ++i) cin >> a[i]; }
template <class T> void input(T* a, int n) { for (int i = 0; i < n; ++i) cin >> a[i]; }

void fix_pre(int n) { cout.setf(ios::fixed, ios::floatfield); cout.precision(10); }
void fast_io() { cin.tie(0); ios::sync_with_stdio(false); }
#define trace(x) (cout << #x << ": " << (x) << endl)
 
bool in_rect(int x, int y, int w, int h) { return 0 <= x && x < w && 0 <= y && y < h; }
 

typedef long long ll;
typedef pair<int, int> pint;
 
// y(v): v>^<  y(^): ^>v<
const int dx[] = { 0, 1, 0, -1 };
const int dy[] = { 1, 0, -1, 0 };

const double PI = acos(-1.0);

#define F first
#define S second



class UnionFind
{
private:
    vector<int> data;
    int _groups;
public:
    int n;
    UnionFind(int n) : data(n, -1), n(n), _groups(n) { }

    void unite(int x, int y)
    {
        x = root(x), y = root(y);
        if (x != y)
        {
            --_groups;
            if (data[x] > data[y])
                swap(x, y);
            data[x] += data[y];
            data[y] = x;
        }
    }
    bool same(int x, int y) { return root(x) == root(y); }
    int root(int x) { return data[x] < 0 ? x : data[x] = root(data[x]); }
    int size(int x) { return -data[root(x)]; }
    int groups() const { return _groups; }
};
int main()
{
    const int M = ten(5) + 100;

    int n, m;
    while (scanf("%d%d", &n, &m), n)
    {
        char query[M];
        int qa[M], qb[M];
        vector<vector<pint> > g(n + 1); // (to, diff)
        rep(i, m)
        {
            char op;
            int a, b;
            scanf(" %c%d%d", &op, &a, &b);
            if (op == '!')
            {
                int w;
                scanf("%d", &w);
                g[a].pb(pint(b, w));
                g[b].pb(pint(a, -w));
            }

            query[i] = op;
            qa[i] = a, qb[i] = b;
        }

        const int undef = ten(9);
        int weight[M];
        fill_n(weight, n + 1, undef);
        for (int s = 1; s <= n; ++s)
        {
            if (weight[s] == undef)
            {
                queue<int> q;
                weight[s] = 0;
                q.push(s);
                while (!q.empty())
                {
                    int v = q.front();
                    q.pop();

                    foreach (it, g[v])
                    {
                        int to = it->first, diff = it->second;
                        if (weight[to] == undef)
                        {
                            weight[to] = weight[v] + diff;
                            q.push(to);
                        }
                    }
                }
            }
        }

        UnionFind uf(n + 1);
        rep(i, m)
        {
            int a = qa[i], b = qb[i];

            if (query[i] == '!')
                uf.unite(a, b);
            else
            {
                if (uf.same(a, b))
                    printf("%d\n", weight[b] - weight[a]);
                else
                    puts("UNKNOWN");
            }
        }
    }
}

Measured memory_bytes: 7084