Example

Input

3 3 1 2 4
1 2
2 3
3 1


Output

IMPOSSIBLE
#include <algorithm>
#include <cmath>
#include <climits>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <fstream>
#include <iostream>
#include <list>
#include <map>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <vector>
#include <cassert>
#include <functional>

using namespace std;

#define LOG(...) printf(__VA_ARGS__)
//#define LOG(...)
#define FOR(i,a,b) for(int i=(int)(a);i<(int)(b);++i)
#define REP(i,n) for(int i=0;i<(int)(n);++i)
#define ALL(a) (a).begin(),(a).end()
#define RALL(a) (a).rbegin(),(a).rend()
#define EXIST(s,e) ((s).find(e)!=(s).end())
#define SORT(c) sort((c).begin(),(c).end())
#define RSORT(c) sort((c).rbegin(),(c).rend())
#define CLR(a) memset((a), 0 ,sizeof(a))

typedef long long ll;
typedef unsigned long long ull;
typedef vector<bool> vb;
typedef vector<int> vi;
typedef vector<ll> vll;
typedef vector<vb> vvb;
typedef vector<vi> vvi;
typedef vector<vll> vvll;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;

const int dx[] = { -1, 0, 1, 0 }; const int dy[] = { 0, 1, 0, -1 };

int main() {
	int n, m;
	vector<int> move(3);
	cin >> n >> m >> move[0] >> move[1] >> move[2];
	SORT(move);
	vector<vector<int>> route(n + 1);

	REP(i, m){
		int a, b;
		cin >> a >> b;
		route[a].push_back(b);
	}
	int ans = -1;
	vector<vector<vector<bool>>> step(n + 1, vector<vector<bool>>(n + 1, vector<bool>(3, false)));
	FOR(i, 1, n){
		vector<int> now;
		now.push_back(i);
		REP(j, move[2]){
			int ns = now.size();
			vector<int> now2;
			set<int> si;
			REP(k, ns){
				REP(l, route[now[k]].size()){
					if (si.find(route[now[k]][l]) == si.end()){
						now2.push_back(route[now[k]][l]);
						si.insert(route[now[k]][l]);
					}
				}
			}
			now = now2;
			if (j == move[0] - 1)
				REP(k, now.size())
				step[i][now[k]][0] = true;
			if (j == move[1] - 1)
				REP(k, now.size())
				step[i][now[k]][1] = true;
			if (j == move[2] - 1)
				REP(k, now.size())
				step[i][now[k]][2] = true;
		}
	}
	vector<vector<int>> goalto(n+1,vector<int>(3,10000));
	goalto[n][0] = 0;
	goalto[n][1] = 0;
	goalto[n][2] = 0;
	queue<pair<int,int>> qii;
	qii.push({ 0,n });
	while (!qii.empty()){
		pair<int,int> num = qii.front(); qii.pop();
		REP(i,n){
			REP(j,3){
				if (step[i][num.second][j]){
					if (goalto[i][j] ==10000){
						goalto[i][j] = num.first + 1;
						if (goalto[i][0] != 10000 && goalto[i][1] != 10000 && goalto[i][2] != 10000){
							qii.push({ max(goalto[i][0], max(goalto[i][1], goalto[i][2])), i });
						}
					}
				}
			}
		}
	}

	REP(i,3){
		if (goalto[1][i] == 10000){
			ans = -1;
			break;
		}
		ans = max(ans, goalto[1][i]);
	}
	if (ans != -1)
		cout << ans << endl;
	else
		cout << "IMPOSSIBLE" << endl;
}