BZOJ 4690 Never Wait for Weights

#include<iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
#define maxn 100500
using namespace std;
int n,m,x,y,z,fath[maxn],dis[maxn];
char s[5];
int getfather(int x)
{
    if (fath[x]==x) return x;
    int ret=getfather(fath[x]);
    dis[x]+=dis[fath[x]];fath[x]=ret;
    return ret;
}
void unionn()
{
    int f1=getfather(x),f2=getfather(y);
    if (f1==f2) return;
    int ret=z+dis[x]-dis[y];
    fath[f2]=f1;dis[f2]=ret;
    return;
}
void ask()
{
    int f1=getfather(x),f2=getfather(y);
    if (f1!=f2) printf("UNKNOWN\n");
    else printf("%d\n",dis[y]-dis[x]);
}
int main()
{
    for (;;)
    {
        scanf("%d%d",&n,&m);
        if ((n==0) || (m==0)) break;
        for (int i=1;i<=n;i++)
        {
            fath[i]=i;
            dis[i]=0;
        }
        for (int i=1;i<=m;i++)
        {
            scanf("%s",s);
            if (s[0]==‘!‘) 
            {
                scanf("%d%d%d",&x,&y,&z);
                unionn();
            }
            else
            {
                scanf("%d%d",&x,&y);
                ask();
            }
        }
    }
    return 0;
}