C++ :

#include<stdio.h>
#include<string.h>
#include<vector>
using namespace std;
const int MAXN = 1000010;
int n, m;
int c[MAXN];
int topo[MAXN], t;
vector <int >G[MAXN];
bool dfs(int u){
  c[u] = -1;
  for(int v = 0; v < n; v++)
  {
    for(vector<int>::iterator it=G[u].begin();it!=G[u].end();it++)
        if(*it==v)
  {
    if(c[v]<0) return false;
    else if(c[v]==0&&!dfs(v)) return    false ;
  }
  }
  c[u] = 1; topo[--t]=u;
  return true;
}
 
bool toposort(){
  t = n;
  memset(c, 0, sizeof(c));
  for(int u = 0; u < n; u++) if(!c[u])
    if(!dfs(u)) return false;
  return true;
}
 
int main() {
  while(scanf("%d%d", &n, &m)!=EOF&&!(n==0&&m==0))
  {
  memset(G, 0, sizeof(G));
  for(int i = 0; i < m; i++) {
    int u, v;
    scanf("%d%d", &u, &v);
    u=u-1;v=v-1;
    G[u].push_back(v);
  }
  if(toposort()) {
    for(int i = 0; i < n; i++)
      printf("%d\n", topo[i]+1);
  }
  else
    printf("IMPOSSIBLE\n");
  }
}