//首先判环我都不会 dfs实在写的戳 后来测了好多数据发现dfs写错了 唉 其次不会哈希啊 这个哈希还是dalao手写给我的 珍惜！！！#include <iostream>
#include <algorithm>
#include <stdio.h>
#include <vector>
#include <string>
#include <string.h>
#include <queue>
#include <math.h>
#include <map>
#define ULL unsigned long long
using namespace std;
const int maxn=10010;
const int INF=0x3f3f3f3f;
#define mod 10007
int cnt;
vector <int> e[10010];//map<ULL,int> mp;
int f[10010];
int de[maxn];
int tot;
bool flag=true;
void dfs(int now){f[now]=-1;for(int i=0;i<e[now].size();i++){if(f[e[now][i]]==-1) {flag=false;}else if(f[e[now][i]]==0) dfs(e[now][i]);}f[now]=1;
}const int maxbuf = 11111;
struct node {ULL key;int id,next;
}buf[maxbuf];
int h[maxn];
ULL fuck(char a[30]){ULL ha=0;for(int i=0;a[i];i++){ha*=52;ha+=a[i];}return (ha);
}
void inithash() {tot = 0;memset(h,-1,sizeof(h));
}
int ins(ULL key) {int now = ++tot;buf[now].key = key, buf[now].id = now, buf[now].next = h[key%mod];h[key%mod] = now;return now;
}
int fnd(ULL key) {for (int i=h[key%mod];~i;i=buf[i].next) {if (buf[i].key == key) return buf[i].id;}return 0;
}char s1[30],s2[30];
int main(){#ifdef shuaishuaifreopen("C:\\Users\\hasee\\Desktop\\trianglen=100000.in","r",stdin);// freopen("C:\\Users\\hasee\\Desktop\\b.txt","w",stdout);// freopen("C:\\Users\\hasee\\Desktop\\picture.in","r",stdin);
#endif// ios::sync_with_stdio(false);char s;int n;memset(f,0,sizeof f);memset(de,0,sizeof de);inithash();while(scanf("%d\n",&n)!=EOF){cnt=1;for(int i=0;i<n;i++){// cout<<"@"<<endl;scanf("%s %c %s\n",s1,&s,s2);
//            cout<<s1<<" "<<s<<" "<<s2<<endl;
ULL x1=fuck(s1);ULL x2=fuck(s2);int u = fnd(x1), v = fnd(x2);//            cout<<"before  "<<u<<" "<<v<<" "<<tot<<endl;
//            cout<<x1<<" "<<x2<<endl;if (!u) u = ins(x1);if (!v) v = ins(x2);
//            printf("%s %d %s %d\n",s1,u,s2,v);
//            cout<<u<<" "<<v<<" "<<tot<<endl;// printf("%d %d\n",x1,x2);//           int x1=mp[t1],x2=mp[t2];
//            if(x1==0)x1=mp[t1]=cnt++;
//            if(x2==0)x2=mp[t2]=cnt++;if(s=='>'){e[u].push_back(v);de[v]++;}else{e[v].push_back(u);de[u]++;}}for(int i=1;i<=tot;i++  ){if(f[i]==0) dfs(i);if(!flag) break;}if(flag)printf("possible\n");elseprintf("impossible\n");for(int i=0;i<=tot;i++)e[i].clear(),f[i]=0,h[i]=-1,de[i]=0;tot=0;}return 0;
}