#include <bits/stdc++.h>
using namespace std;
long long low(vector<long long> &a, long long b) {
  auto c = lower_bound(a.begin(), a.end(), b);
  long long d = c - a.begin();
  return d;
}
long long upp(vector<long long> &a, long long b) {
  auto c = upper_bound(a.begin(), a.end(), b);
  long long d = c - a.begin();
  return d;
}
template <class T>
void cou(vector<vector<T>> a) {
  long long b = a.size();
  long long c = a[0].size();
  for (long long i = 0; i < b; i++) {
    for (long long j = 0; j < c; j++) {
      cout << a[i][j];
      if (j == c - 1)
        cout << endl;
      else
        cout << ' ';
    }
  }
}
long long wari(long long a, long long b) {
  if (a % b == 0)
    return a / b;
  else
    return a / b + 1;
}
long long keta(long long a) {
  long double b = a;
  b = log10(b);
  long long c = b;
  return c + 1;
}
long long souwa(long long a) { return a * (a + 1) / 2; }
long long gcm(long long a, long long b) {
  if (a % b == 0) return b;
  return gcm(b, a % b);
}
bool prime(long long a) {
  if (a < 2)
    return false;
  else if (a == 2)
    return true;
  else if (a % 2 == 0)
    return false;
  for (long long i = 3; i <= sqrt(a) + 1; i += 2) {
    if (a % i == 0) return false;
  }
  return true;
}
struct Union {
  vector<long long> par;
  Union(long long a) { par = vector<long long>(a, -1); }
  long long find(long long a) {
    if (par[a] < 0)
      return a;
    else
      return par[a] = find(par[a]);
  }
  bool same(long long a, long long b) { return find(a) == find(b); }
  long long Size(long long a) { return -par[find(a)]; }
  void unite(long long a, long long b) {
    a = find(a);
    b = find(b);
    if (a == b) return;
    if (Size(b) > Size(a)) swap<long long>(a, b);
    par[a] += par[b];
    par[b] = a;
  }
};
long long ketas(long long a) {
  string b = to_string(a);
  long long c = 0;
  for (long long i = 0; i < keta(a); i++) {
    c += b[i] - '0';
  }
  return c;
}
bool fe(long long a, long long b) {
  a %= 10;
  b %= 10;
  if (a == 0) a = 10;
  if (b == 0) b = 10;
  if (a > b)
    return true;
  else
    return false;
}
long long INF = 1000000007;
struct edge {
  long long s, t, d;
};
vector<long long> mojisyu(string a) {
  vector<long long> b(26, 0);
  for (long long i = 0; i < a.size(); i++) {
    b[a[i] - 'a']++;
  }
  return b;
}
long long wa2(long long a) {
  if (a % 2 == 1) return a / 2;
  return a / 2 - 1;
}
long long nCr(long long n, long long r) {
  long long a = 1;
  r = min(r, n - r);
  for (long long i = n; i > n - r; i--) {
    a *= i;
    a /= n - i + 1;
  }
  return a;
}
long long kaijou(long long a) {
  long long b = 1;
  for (long long i = 0; i < a; i++) b *= i + 1;
  return b;
}
long long nPr(long long a, long long b) {
  if (a < b) return 0;
  if (b == 0) return 1;
  long long c = 1;
  for (long long i = a; i > a - b; i--) {
    c *= i;
    c %= INF;
  }
  return c;
}
long long modpow(long long a, long long n, long long mod) {
  long long res = 1;
  while (n > 0) {
    if (n & 1) res = res * a % mod;
    a = a * a % mod;
    n >>= 1;
  }
  return res;
}
long long modinv(long long a, long long mod) { return modpow(a, mod - 2, mod); }
long long lcm(long long a, long long b) {
  long long c = modinv(gcm(a, b), INF);
  return ((a * c) % INF) * (b % INF) % INF;
}
long long MOD = INF;
long long fac[1000010], finv[1000010], inv[1000010];
void COMinit() {
  fac[0] = fac[1] = 1;
  finv[0] = finv[1] = 1;
  inv[1] = 1;
  for (long long i = 2; i < 1000010; i++) {
    fac[i] = fac[i - 1] * i % MOD;
    inv[i] = MOD - inv[MOD % i] * (MOD / i) % MOD;
    finv[i] = finv[i - 1] * inv[i] % MOD;
  }
}
long long COM(long long n, long long k) {
  if (n < k) return 0;
  if (n < 0 || k < 0) return 0;
  return fac[n] * (finv[k] * finv[n - k] % MOD) % MOD;
}
bool naka(long long a, long long b, vector<vector<char>> c) {
  return (a >= 0 && b >= 0 && a < c.size() && b < c[0].size());
}
vector<pair<long long, long long>> mawari8 = {
    {0, -1}, {0, 1}, {1, 0}, {-1, 0}, {-1, -1}, {1, 1}, {1, -1}, {-1, -1}};
long long inf = 1000000000000000007;
vector<pair<long long, long long>> mawari4 = {{0, -1}, {0, 1}, {1, 0}, {-1, 0}};
vector<long long> onajibubun(string a) {
  vector<long long> b(a.size());
  for (long long i = 1, j = 0; i < a.size(); i++) {
    if (i + b[i - j] < j + b[j])
      b[i] = b[i - j];
    else {
      long long c = max<long long>(0, j + b[j] - i);
      while (i + c < a.size() && a[c] == a[i + c]) c++;
      b[i] = c;
      j = i;
    }
  }
  b[0] = a.size();
  return b;
}
vector<long long> color(205);
bool nibu_hantei(long long a, long long b, vector<vector<long long>> c) {
  color[a] = b;
  for (long long i = 0; i < c[a].size(); i++) {
    if (b == color[c[a][i]]) return false;
    if (color[c[a][i]] == 0 && !nibu_hantei(c[a][i], -b, c)) return false;
  }
  return true;
}
bool renketujanai_nibu_hantei(long long a, vector<vector<long long>> c) {
  for (long long i = 0; i < a; i++) {
    if (color[i] == 0) {
      if (!nibu_hantei(i, 1, c)) return false;
    }
  }
  return true;
}
struct segmin {
  vector<long long> seg;
  long long b;
  segmin(vector<long long> a) {
    b = 1;
    while (b < a.size()) b *= 2;
    seg = vector<long long>(2 * b - 1, inf);
    for (long long i = 0; i < a.size(); i++) {
      seg[i + b - 1] = a[i];
    }
    for (long long i = b - 2; i >= 0; i--) {
      seg[i] = min(seg[2 * i + 1], seg[2 * i + 2]);
    }
  }
  void update(long long i, long long a) {
    i += b - 1;
    seg[i] = a;
    while (i) {
      i = (i - 1) / 2;
      seg[i] = min(seg[2 * i + 1], seg[2 * i + 2]);
    }
  }
  long long getmin(long long x, long long y, long long a, long long l,
                   long long r) {
    if (r == INF) r = b;
    if (r <= x || y <= l) return INF;
    if (x <= l && r <= y) return seg[a];
    long long a1 = getmin(x, y, 2 * a + 1, l, (l + r) / 2);
    long long a2 = getmin(x, y, 2 * a + 2, (l + r) / 2, r);
    return min(a1, a2);
  }
};
struct segadd {
  vector<long long> seg;
  long long b;
  segadd(vector<long long> a) {
    b = 1;
    while (b < a.size()) b *= 2;
    seg = vector<long long>(2 * b - 1, 0);
    for (long long i = 0; i < a.size(); i++) {
      seg[i + b - 1] = a[i];
    }
    for (long long i = b - 2; i >= 0; i--) {
      seg[i] = seg[2 * i + 1] + seg[2 * i + 2];
    }
  }
  void update(long long i, long long a) {
    i += b - 1;
    seg[i] = a;
    while (i) {
      i = (i - 1) / 2;
      seg[i] = seg[2 * i + 1] + seg[2 * i + 2];
    }
  }
  long long getadd(long long x, long long y, long long a, long long l,
                   long long r) {
    if (r == INF) r = b;
    if (r <= x || y <= l) return 0;
    if (x <= l && r <= y) return seg[a];
    long long a1 = getadd(x, y, 2 * a + 1, l, (l + r) / 2);
    long long a2 = getadd(x, y, 2 * a + 2, (l + r) / 2, r);
    return a1 + a2;
  }
};
struct segtako {
  vector<pair<long double, long double>> seg;
  long long b;
  segtako(long long a) {
    b = 1;
    while (b < a) b *= 2;
    seg = vector<pair<long double, long double>>(2 * b - 1, {1, 0});
    for (long long i = 0; i < a; i++) {
      seg[i + b - 1] = {1, 0};
    }
    for (long long i = b - 2; i >= 0; i--) {
      seg[i] = {
          seg[2 * i + 1].first * seg[2 * i + 2].first,
          seg[2 * i + 1].second * seg[2 * i + 2].first + seg[2 * i + 2].second};
    }
  }
  void update(long long i, pair<long double, long double> a) {
    i += b - 1;
    seg[i] = a;
    while (i) {
      i = (i - 1) / 2;
      seg[i] = {
          seg[2 * i + 1].first * seg[2 * i + 2].first,
          seg[2 * i + 1].second * seg[2 * i + 2].first + seg[2 * i + 2].second};
    }
  }
  long double gettako() { return seg[0].first + seg[0].second; }
};
signed main() {
  long long a, b;
  cin >> a >> b;
  vector<pair<long long, long long>> c(b);
  for (long long i = 0; i < b; i++) cin >> c[i].first >> c[i].second;
  sort(c.begin(), c.end());
  for (long long i = 0; i < b - 1; i++) {
    if (c[i].first == c[i + 1].first && c[i].second != c[i + 1].second) {
      cout << -1 << endl;
      return 0;
    }
  }
  if (c.size()) {
    if (c[0].first == 1 && c[0].second == 0) {
      cout << -1 << endl;
      return 0;
    }
  }
  c.erase(unique(c.begin(), c.end()), c.end());
  long long d = 0;
  for (long long i = 0; i < a; i++) {
    if (d < c.size()) {
      if (i == c[d].first - 1) {
        cout << c[d].second;
        d++;
      } else
        cout << 0;
    } else
      cout << 0;
  }
  cout << endl;
}
