#include <bits/stdc++.h>
#define endl '\n'
#define ALL(v) std::begin(v), std::end(v)
#define ALLR(v) std::rbegin(v), std::rend(v)
using ll = std::int64_t;
using ull = std::uint64_t;
using pll = std::pair<ll, ll>;
using tll = std::tuple<ll, ll, ll>;
template <typename T> using vec = std::vector<T>;
template <typename T> using vvec = vec<vec<T>>;
template <typename T> const T& var_min(const T &t) { return t; }
template <typename T> const T& var_max(const T &t) { return t; }
template <typename T, typename... Tail> const T& var_min(const T &t, const Tail&... tail) { return std::min(t, var_min(tail...)); }
template <typename T, typename... Tail> const T& var_max(const T &t, const Tail&... tail) { return std::max(t, var_max(tail...)); }
template <typename T, typename... Tail> void chmin(T &t, const Tail&... tail) { t = var_min(t, tail...); }
template <typename T, typename... Tail> void chmax(T &t, const Tail&... tail) { t = var_max(t, tail...); }
template <typename T> const T& clamp(const T &t, const T &low, const T &high) { return std::max(low, std::min(high, t)); }
template <typename T> void chclamp(T &t, const T &low, const T &high) { return t = clamp(t, low, high); }
namespace init__ { struct InitIO { InitIO() { std::cin.tie(nullptr); std::ios_base::sync_with_stdio(false); std::cout << std::fixed << std::setprecision(30); } } init_io; }
#define mv_rec make_v(init, tail...)
template <typename T> T make_v(T init) { return init; }
template <typename T, typename... Tail> auto make_v(T init, size_t s, Tail... tail) { return vec<decltype(mv_rec)>(s, mv_rec); }
#undef mv_rec


using namespace std;

string solve() {
    ll n, m;
    cin >> n >> m;
    vec<bool> decide(n, false);
    string ans(n, '0');
    ans[0] = '1';
    for (ll i = 0; i < m; i++) {
        ll s, c;
        cin >> s >> c;
        s--;
        char nc = '0' + c;
        if (s == 0 && c == 0) return "-1";
        if (!decide[s]) {
            ans[s] = nc;
            decide[s] = true;
        } else {
            if (ans[s] == nc) continue;
            return "-1";
        }
    }
    return ans;
}

int main() {
    cout << solve() << endl;
    return 0;
}
