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

int main() {
    static const int maxn = 400010;
    int n, m;
    scanf("%d %d", &n, &m);
    static int b[maxn], e[maxn];
    for (int i = 1; i <= n; i++) scanf("%d %d", b + i, e + i);
    static vector<int> G[maxn];
    while (m--) {
        int x, y;
        scanf("%d %d", &x, &y);
        G[x].push_back(y);
        G[y].push_back(x);
    }
    static vector<int> vec[maxn];
    static int bel[maxn], siz[maxn], cnt;
    function<void(int, int)> tarjan = [&tarjan](const int u, const int fa) {
        static stack<int> S;
        static int dfn[maxn], low[maxn], c;
        S.push(u), dfn[u] = low[u] = ++c;
        for (int i : G[u])
            if (i != fa) {
                if (!dfn[i])
                    tarjan(i, u), low[u] = min(low[u], low[i]);
                else if (!bel[i])
                    low[u] = min(low[u], dfn[i]);
            }
        if (dfn[u] == low[u]) {
            int v;
            cnt++;
            do bel[v = S.top()] = cnt, vec[cnt].push_back(v), S.pop();
            while (v != u);
        }
        return;
    };
    for (int i = 1; i <= n; i++)
        if (!bel[i])
            tarjan(i, 0);
    for (int i = 1; i <= n; i++)
        for (int j : G[i])
            if (i < j && bel[i] == bel[j])
                siz[bel[i]]++;
    auto get = [](const vector<int>& a) {
        int i = 0, j = 1, k = 0;
        while (i < a.size() && j < a.size() && k < a.size()) {
            int I = a[(i + k) % a.size()], J = a[(j + k) % a.size()];
            I != J ? (I > J ? i : j) += k + 1, j += i == j, k = 0 : k++;
        }
        i = min(i, j);
        vector<int> ret;
        for (int p = i; p < a.size(); p++) ret.push_back(a[p]);
        for (int p = 0; p < i; p++) ret.push_back(a[p]);
        return ret;
    };
    for (int i = 1; i <= cnt; i++)
        if (siz[i] == vec[i].size()) {
            vector<int> B, E;
            for (int u : vec[i]) B.push_back(b[u]), E.push_back(e[u]);
            if (get(B) != get(E)) {
                printf("impossible\n");
                return 0;
            }
        }
    printf("possible\n");
    return 0;
}