#include<iostream>

using namespace std;

const int maxn = 100005;

int fa[maxn],val[maxn];

int find_(int x){

    if(x != fa[x])

    {

        int t=fa[x];

        fa[x]=find_(fa[x]);

        val[x]+=val[t];

        return fa[x];

    }//路径压缩

    return x;

}

void merge_(int a,int b,int c){

    int fx,fy;

    fx=find_(a);

    fy=find_(b);

    if(fx != fy)

    {

        fa[fx]=fy;

        val[fx]=val[b]+c-val[a];

    }

}

int main(){

    int n,m;

    while(cin>>n>>m&&n&&m){

       char t;

       int a,b,c;

       for(int i=1;i<=m;i++)

        fa[i]=i,val[i]=0;

       while(m--){

        cin>>t>>a>>b;

        if(t == '!')

        {

            cin>>c;

            merge_(a,b,c);

        }

        else

        {

            int fx,fy;

            fx=find_(a),fy=find_(b);

            if(fx != fy)

            cout<<"UNKNOWN"<<endl;

            else

            cout<<val[a]-val[b]<<endl;

        }

       }

    }

}