// SmartCoder
#include <bits/stdc++.h>

#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>  // Including tree_order_statistics_node_update

using namespace __gnu_pbds;
using namespace std;

#define sz(a) int((a).size())
#define pb push_back
#define mp make_pair
#define all(c) (c).begin(), (c).end()
#define tr(c, i) for (__typeof((c).begin()) i = (c).begin(); i != (c).end(); i++)
#define present(c, x) ((c).find(x) != (c).end())
#define cpresent(c, x) (find(all(c), x) != (c).end())
#define minei(x) min_element(x.begin(), x.end()) - (x).begin()
#define maxei(x) max_element(x.begin(), x.end()) - (x).begin()
#define LSOne(S) (S & (-S))

#define uns(v) sort((v).begin(), (v).end()), v.erase(unique(v.begin(), v.end()), v.end())
#define acusum(x) accumulate(x.begin(), x.end(), 0)
#define acumul(x) accumulate(x.begin(), x.end(), 1, multiplies<int>());
#define bits(x) __builtin_popcount(x)
#define oo INT_MAX
#define inf 1000000000
#define MAXN 1000007
#define MOD 1000000007

const double pi = acos(-1.0);
const double eps = 1e-11;

typedef long long ll;
typedef pair<int, int> ii;
typedef vector<ii> vii;
typedef vector<int> vi;
typedef tree<int, null_type, less<int>, rb_tree_tag, tree_order_statistics_node_update> indexed_set;

int main() {
    std::ios_base::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);
    int n, m, s, c;
    cin >> n >> m;
    vector<int> nm(n, -1);
    bool found = true;
    for (int i = 0; i < m; i++) {
        cin >> s >> c;
        s--;
        if (nm[s] != -1 && (nm[s] != c)) {
            found = false;
        }
        nm[s] = c;
    }
    if (!found) {
        cout << "-1\n";
        return 0;
    }
    if (n == 1) {
        cout << (nm[s] == -1 ? 0 : nm[s]) << "\n";
    }
    if (n == 2) {
        if (nm[0] == 0) {
            cout << "-1\n";
            return 0;
        }
        if (nm[0] == -1) nm[0] = 1;
        if (nm[1] == -1) nm[1] = 0;
        cout << nm[0] * 10 + nm[1] << "\n";
    }
    if (n == 3) {
        if (nm[0] == 0) {
            cout << "-1\n";
            return 0;
        }
        if (nm[0] == -1) nm[0] = 1;
        if (nm[1] == -1) nm[1] = 0;
        if (nm[2] == -1) nm[2] = 0;
        cout << nm[0] * 100 + nm[1] * 10 + nm[2] << "\n";
    }

    return 0;
}
