#include <bits/stdc++.h>
using namespace std;

template<class T>
bool chmax(T& a, const T& b) {
    if (a < b) { a = b; return true; }
    return false;
}
template<class T>
bool chmin(T& a, const T& b) {
    if (b < a) { a = b; return true; }
    return false;
}

// std::vector Declaration
template<typename T>
vector<T> make_v(size_t a) { return vector<T>(a); }
template<typename T, typename... Ts>
auto make_v(size_t a, Ts... ts) {
    return vector<decltype(make_v<T>(ts...))>(a, make_v<T>(ts...));
}

// std::vector Declaration and Initialization
template<typename T>
vector<T> make_vector(size_t a, T x) { return vector<T>(a, x); }
template<typename T, typename U, typename... Ts>
auto make_vector(size_t a, U b, Ts... ts) {
    return vector<decltype(make_vector<T>(b,ts...))>(a, make_vector<T>(b, ts...));
}

// std::vector Input
template<typename T>
istream& operator>>(istream& is, vector<T>& v) {
    for (auto &e : v) is >> e;
    return is;
}

// std::vector Debug
template<typename T>
ostream& operator<<(ostream& os, const vector<T>& v) {
    os << "[";
    bool a = 1;
    for (auto e : v) {
        os << (a ? "" : " ");
        os << e;
        a = 0;
    }
    os << "]";
    return os;
}

// std::array Debug
template<typename T, size_t n>
ostream& operator<<(ostream& os, const array<T, n>& v) {
    os << "[";
    bool a = 1;
    for (auto e : v) {
        os << (a ? "" : " ");
        os << e;
        a = 0;
    }
    os << "]";
    return os;
}

// std::deque Debug
template<typename T>
ostream& operator<<(ostream& os, const deque<T>& d) {
    os << "[";
    bool a = 1;
    for (auto e : d) {
        os << (a ? "" : " ");
        os << e;
        a = 0;
    }
    os << "]";
    return os;
}

// std::pair Debug
template<typename T, typename U>
ostream& operator<<(ostream& os, const pair<T, U>& p) {
    os << "(" << p.first << " " << p.second << ")";
    return os;
}

// std::set Debug
template<typename T>
ostream& operator<<(ostream& os, const set<T>& st) {
    os << "{";
    bool a = 1;
    for (auto e : st) {
        os << (a ? "" : " ");
        os << e;
        a = 0;
    }
    os << "}";
    return os;
}

// std::multiset Debug
template<typename T>
ostream& operator<<(ostream& os, const multiset<T>& st) {
    os << "{";
    bool a = 1;
    for (auto e : st) {
        os << (a ? "" : " ");
        os << e;
        a = 0;
    }
    os << "}";
    return os;
}

// std::map Debug
template<typename T, typename U>
ostream& operator<<(ostream& os, const map<T, U>& mp) {
    os << "{";
    bool a = 1;
    for (auto e : mp) {
        os << (a ? "" : " ");
        os << e.first << ":" << e.second;
        a = 0;
    }
    os << "}";
    return os;
}

// std::tuple Debug
template<int N, class Tuple>
void out(ostream& os, const Tuple& t){}
template<int N, class Tuple, class H, class ...Ts>
void out(ostream& os, const Tuple& t) {
    if (N) os << " ";
    os << get<N>(t);
    out<N+1,Tuple,Ts...>(os, t);
}
template<class ...Ts>
ostream& operator<<(ostream& os, const tuple<Ts...>& t) {
    os << "(";
    out<0,tuple<Ts...>,Ts...>(os, t);
    os << ")";
    return os;
}

// Debug
#define DUMP(x) cerr<<#x<<" = "<<(x)<<endl

// Weighted edge
template<typename T>
struct edge {
    int src, to;
    T cost;

    edge() {}
    edge(int to, T cost) : src(-1), to(to), cost(cost) {}
    edge(int src, int to, T cost) : src(src), to(to), cost(cost) {}

    friend ostream& operator<<(ostream& os, const edge& e) {
        return os << "(" << e.src << "->" << e.to << ":" << e.cost << ")";
    }
};

using LL = int64_t;

#define fs first
#define sc second

const int64_t MOD = 1e9+7;


template<typename T>
vector<T> dijkstra(const vector<vector<edge<T>>> &g, int s) {
    const T INF = numeric_limits<T>::max();
    vector<T> d(g.size(), INF);

    using Pi = pair<T, int>;
    priority_queue<Pi, vector<Pi>, greater<Pi>> que;
    d[s] = 0;
    que.emplace(d[s], s);
    while (!que.empty()) {
        T cost;
        int v;
        tie(cost, v) = que.top();
        que.pop();
        if (d[v] < cost) continue;
        for (auto &e : g[v]) {
            T nxt = cost + e.cost;
            if (d[e.to] > nxt) {
                d[e.to] = nxt;
                que.emplace(nxt, e.to);
            }
        }
    }
    return d;
}


int main()
{
    cin.tie(0);
    ios::sync_with_stdio(false);
    cout << fixed << setprecision(10);

    int n, m, a, b, c;
    cin >> n >> m >> a >> b >> c;
    vector<vector<int>> G(n);
    for (int i = 0; i < m; ++i) {
        int u, v; cin >> u >> v; --u, --v;
        G[u].push_back(v);
    }

    const int MAX = 100;
    vector<array<vector<int>,3>> g(n);

    for (int s = 0; s < n; ++s) {
        vector<bitset<MAX+1>> bit(n);
        bit[s].set(0);
        for (int k = 0; k < MAX; ++k) {
            for (int i = 0; i < n; ++i) {
                for (int u : G[i]) {
                    bit[u] |= bit[i] << 1;
                }
            }
        }
        for (int i = 0; i < n; ++i) {
            if (bit[i][a]) g[s][0].push_back(i);
            if (bit[i][b]) g[s][1].push_back(i);
            if (bit[i][c]) g[s][2].push_back(i);
        }
    }

    const int INF = numeric_limits<int>::max();
    vector<int> cost(n, INF);
    cost[n-1] = 0;
    for (int t = 0; t < n; ++t) {
        for (int i = 0; i < n; ++i) {
            int maxCost = 0;
            for (int k = 0; k < 3; ++k) {
                int minCost = INF;
                for (int u : g[i][k]) if (cost[u] != INF) {
                    chmin(minCost, cost[u] + 1);
                }
                chmax(maxCost, minCost);
            }
            chmin(cost[i], maxCost);
        }
    }

    if (cost[0] == INF) {
        cout << "IMPOSSIBLE" << endl;
    } else {
        cout << cost[0] << endl;
    }


    return 0;
}



Measured memory_bytes: 3244