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

// Define
using ll = long long;
using ull = unsigned long long;
using ld = long double;
template <class T> using pvector = vector<pair<T, T>>;
template <class T>
using rpriority_queue = priority_queue<T, vector<T>, greater<T>>;
constexpr const ll dx[4] = {1, 0, -1, 0};
constexpr const ll dy[4] = {0, 1, 0, -1};
constexpr const ll MOD = 1e9 + 7;
constexpr const ll mod = 998244353;
constexpr const ll INF = 1LL << 60;
constexpr const ll inf = 1 << 30;
constexpr const char rt = '\n';
constexpr const char sp = ' ';
#define mp make_pair
#define mt make_tuple
#define pb push_back
#define eb emplace_back
#define elif else if
#define all(a, v, ...)                                                         \
    ([&](decltype((v)) w) { return (a)(begin(w), end(w), ##__VA_ARGS__); })(v)
#define rall(a, v, ...)                                                        \
    ([&](decltype((v)) w) { return (a)(rbegin(w), rend(w), ##__VA_ARGS__); })(v)
#define fi first
#define se second

template <class T> bool chmax(T &a, const T &b) {
    if (a < b) {
        a = b;
        return 1;
    }
    return 0;
}
template <class T> bool chmin(T &a, const T &b) {
    if (a > b) {
        a = b;
        return 1;
    }
    return 0;
}

// Debug
#define debug(...)                                                             \
    {                                                                          \
        cerr << __LINE__ << ": " << #__VA_ARGS__ << " = ";                     \
        for (auto &&X : {__VA_ARGS__}) cerr << "[" << X << "] ";               \
        cerr << rt;                                                            \
    }

#define dump(a, h, w)                                                          \
    {                                                                          \
        cerr << __LINE__ << ": " << #a << " = [" << rt;                        \
        rep(_i, h) {                                                           \
            rep(_j, w) cerr << a[_i][_j] << sp;                                \
            cerr << rt;                                                        \
        }                                                                      \
        cerr << "]" << rt;                                                     \
    }

#define vdump(a, n)                                                            \
    {                                                                          \
        cerr << __LINE__ << ": " << #a << " = [";                              \
        rep(_i, n) if (_i) cerr << sp << a[_i];                                \
        else cerr << a[_i];                                                    \
        cerr << "]" << rt;                                                     \
    }

// Loop
#define inc(i, a, n) for (ll i = (a), _##i = (n); i <= _##i; ++i)
#define dec(i, a, n) for (ll i = (a), _##i = (n); i >= _##i; --i)
#define rep(i, n) for (ll i = 0, _##i = (n); i < _##i; ++i)
#define each(i, a) for (auto &&i : a)

// Stream
#define fout(n) cout << fixed << setprecision(n)
struct io {
    io() { cin.tie(nullptr), ios::sync_with_stdio(false); }
} io;

// Speed
#pragma GCC optimize("Ofast")
#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,tune=native")

// Math
inline constexpr ll gcd(const ll a, const ll b) {
    return b ? gcd(b, a % b) : a;
}
inline constexpr ll lcm(const ll a, const ll b) { return a / gcd(a, b) * b; }

inline constexpr ll modulo(const ll n, const ll m = MOD) {
    ll k = n % m;
    return k + m * (k < 0);
}
inline constexpr ll chmod(ll &n, const ll m = MOD) {
    n %= m;
    return n += m * (n < 0);
}
inline constexpr ll mpow(ll a, ll n, const ll m = MOD) {
    ll r = 1;
    rep(i, 64) {
        if (n & (1LL << i)) r *= a;
        chmod(r, m);
        a *= a;
        chmod(a, m);
    }
    return r;
}
inline ll inv(const ll n, const ll m = MOD) {
    ll a = n, b = m, x = 1, y = 0;
    while (b) {
        ll t = a / b;
        a -= t * b;
        swap(a, b);
        x -= t * y;
        swap(x, y);
    }
    return modulo(x, m);
}

namespace Kika {
using Double = long double;
const Double EPS = 1e-20l;
const Double M_PIL = 3.1415926535897932384626433832795028841971693993751l;
bool equals(Double a, Double b) { return fabsl(a - b) < EPS; }
struct Point {
    Double x, y;
    Point(Double x = 0, Double y = 0) : x(x), y(y) {}
    Point operator+(Point p) { return Point(x + p.x, y + p.y); }
    Point operator-(Point p) { return Point(x - p.x, y - p.y); }
    Point operator*(Double a) { return Point(a * x, a * y); }
    Point operator/(Double a) { return Point(x / a, y / a); }
    Point operator+=(Point p) {
        x += p.x, y += p.y;
        return *this;
    }
    Point operator-=(Point p) {
        x -= p.x, y -= p.y;
        return *this;
    }
    Point operator*=(Double a) {
        x *= a, y *= a;
        return *this;
    }
    Point operator/=(Double a) {
        x /= a, y /= a;
        return *this;
    }
    bool operator<(const Point &p) const {
        return x != p.x ? x < p.x : y < p.y;
    }
    bool operator==(const Point &p) const {
        return fabsl(x - p.x) < EPS and fabsl(y - p.y) < EPS;
    }
    Double abs() { return sqrtl(norm()); }
    Double norm() { return x * x + y * y; }
};
using Vector = Point;
struct Segment {
    Point p1, p2;
};
using Line = Segment;
struct Circle {
    Point c;
    Double r;
    Circle(Point c = Point(), Double r = 0.0l) : c(c), r(r) {}
};
using Polygon = vector<Point>;

enum ccw_status {
    COUNTER_CLOCKWISE = 1,
    CLOCKWISE = -1,
    ONLINE_BACK = 2,
    ONLINE_FRONT = -2,
    ON_SEGMENT = 0
};

enum contains_status { IN = 2, ON = 1, OUT = 0 };

Point operator*(Double a, Point p) { return Point(a * p.x, a * p.y); }
Point operator/(Double a, Point p) { return Point(p.x / a, p.y / a); }
Double abs(Vector a) { return a.x * a.x + a.y * a.y; }
Double norm(Vector a) { return sqrtl(abs(a)); }
Double dot(Vector a, Vector b) { return a.x * b.x + a.y * b.y; }
Double cross(Vector a, Vector b) { return a.x * b.y - a.y * b.x; }
Double sin(Vector a, Vector b) { return cross(a, b) / a.norm() / b.norm(); }
Double cos(Vector a, Vector b) { return dot(a, b) / a.norm() / b.norm(); }
Double arg(Vector p) { return atan2l(p.y, p.x); }
Double angle(Vector a, Vector b) {
    Double theta = arg(b) - arg(a);
    while (theta < -M_PIL + EPS) theta += 2.0l * M_PIL;
    while (theta > M_PIL + EPS) theta -= 2.0l * M_PIL;
    return theta;
}
Vector polar(Double a, Double r) { return Point(a * cosl(r), a * sinl(r)); }
bool isOrthogonal(Vector a, Vector b) { return equals(dot(a, b), 0.0l); }
bool isOrthogonal(Point a1, Point a2, Point b1, Point b2) {
    return isOrthogonal(a2 - a1, b2 - b1);
}
bool isOrthogonal(Segment s1, Segment s2) {
    return equals(dot(s1.p2 - s1.p1, s2.p2 - s2.p1), 0.0l);
}
bool isParallel(Vector a, Vector b) { return equals(cross(a, b), 0.0l); }
bool isParallel(Point a1, Point a2, Point b1, Point b2) {
    return isParallel(a2 - a1, b2 - b1);
}
bool isParallel(Segment s1, Segment s2) {
    return equals(cross(s1.p2 - s1.p1, s2.p2 - s2.p1), 0.0l);
}
ccw_status ccw(Point p0, Point p1, Point p2) {
    Vector a = p1 - p0;
    Vector b = p2 - p0;
    if (cross(a, b) > EPS) return COUNTER_CLOCKWISE;
    if (cross(a, b) < -EPS) return CLOCKWISE;
    if (dot(a, b) < -EPS) return ONLINE_BACK;
    if (a.norm() > b.norm()) return ONLINE_FRONT;
    return ON_SEGMENT;
}
bool intersect(Point p1, Point p2, Point p3, Point p4) {
    return ccw(p1, p2, p3) * ccw(p1, p2, p4) <= 0 and
           ccw(p3, p4, p1) * ccw(p3, p4, p2) <= 0;
}
bool intersect(Segment s1, Segment s2) {
    return intersect(s1.p1, s1.p2, s2.p1, s2.p2);
}
Point project(Segment s, Point p) {
    Vector base = s.p2 - s.p1;
    Double r = dot(p - s.p1, base) / norm(base);
    return s.p1 + base * r;
}
Point reflect(Segment s, Point p) { return p + 2.0l * (project(s, p) - p); }
Double distance(Point a, Point b) { return abs(b - a); }
Double distanceLP(Line l, Point p) {
    return cross(l.p2 - l.p1, p - l.p1) / abs(l.p2 - l.p1);
}
Double distanceSP(Segment s, Point p) {
    if (cross(s.p2 - s.p1, p - s.p1) < 0.0l) return abs(p - s.p1);
    if (cross(s.p1 - s.p2, p - s.p2) < 0.0l) return abs(p - s.p2);
    return distanceLP(s, p);
}
Double distance(Segment s1, Segment s2) {
    if (intersect(s1, s2)) return 0.0l;
    return min(min(distanceSP(s1, s2.p1), distanceSP(s1, s2.p2)),
               min(distanceSP(s2, s1.p1), distanceSP(s2, s1.p2)));
}
Point crossPoint(Segment s1, Segment s2) {
    Vector base = s2.p2 - s1.p1;
    Double d1 = abs(cross(base, s1.p1 - s2.p1));
    Double d2 = abs(cross(base, s1.p2 - s2.p1));
    Double t = d1 / (d1 + d2);
    return s1.p1 + (s1.p2 - s1.p1) * t;
}
bool intersect(Circle c, Line l) { return distanceLP(l, c.c) <= c.r; }
bool intersect(Circle c1, Circle c2) {
    return distance(c1.c, c2.c) <= c1.r + c2.r;
}
pair<Point, Point> crossPoints(Circle c, Line l) {
    assert(intersect(c, l));
    Vector pr = project(l, c.c);
    Vector e = (l.p2 - l.p1) / abs(l.p2 - l.p1);
    Double base = sqrtl(c.r * c.r - norm(pr - c.c));
    return make_pair(pr + e * base, pr - e * base);
}
pair<Point, Point> crossPoints(Circle c1, Circle c2) {
    assert(intersect(c1, c2));
    Double d = abs(c2.c - c1.c);
    Double a = acosl((c1.r * c1.r + d * d - c2.r * c2.r) / (2.0l * c1.r * d));
    Double t = arg(c2.c - c1.c);
    return make_pair(c1.c + polar(c1.r, t + a), c1.c + polar(c1.r, t - a));
}
contains_status contains(Polygon g, Point p) {
    ll n = g.size();
    bool x = false;
    rep(i, n) {
        Point a = g[i] - p, b = g[(i + 1) % n] - p;
        if (abs(cross(a, b)) < EPS and dot(a, b) < EPS) return ON;
        if (a.y > b.y) swap(a, b);
        if (a.y < EPS and EPS < b.y and cross(a, b) > EPS) x = !x;
    }
    return x ? OUT : IN;
}

istream &operator>>(istream &is, Point &p) {
    is >> p.x >> p.y;
    return is;
}
ostream &operator<<(ostream &os, const Point &p) {
    os << '(' << p.x << ", " << p.y << ")";
    return os;
}
} // namespace Kika

signed main() {
    ll N, M;
    cin >> N >> M;
    ll A[N], B, C;
    rep(i, N) A[i] = -1;
    rep(i, M) {
        cin >> B >> C;
        if (A[B - 1] != -1 and A[B - 1] != C) {
            return puts("-1") & 0;
        }
        A[B - 1] = C;
    }
    if (A[0] == 0 and N != 1) return puts("-1") & 0;
    rep(i, N) {
        if (A[i] == -1) {
            cout << (i == 0 ? 1 : 0);
        } else {
            cout << A[i];
        }
    }
    cout << rt;
}

// -g -D_GLIBCXX_DEBUG -fsanitize=undefined
