// INCLUDES
#include <bits/stdc++.h>
#include <assert.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
//DEFINES
#define MAX 1000001
#define pii pair<int, int>
#define c1 __builtin_popcount
#define F first
#define S second
#define all(s) begin(s), end(s)
#define MIN3POS(a, b, c) (a) = < (b) ? ((a) = < (c) ? 1 : 3) : ((b) = < (c) ? 2 : 3)
#define MAX3POS(a, b, c) (a) >= (b) ? ((a) >= (c) ? 1 : 3) : ((b) >= (c) ? 2 : 3)
#define endl '\n'
#define int long long
#define ordered_set tree<int, null_type, less<int>, rb_tree_tag, tree_order_statistics_node_update>
#define FOR(i, begin, end) for (__typeof(end) i = (begin) - ((begin) > (end)); i != (end) - ((begin) > (end)); i += 1 - 2 * ((begin) > (end)))
#define IOS                           \
    ios_base::sync_with_stdio(false); \
    cin.tie(0);                       \
    cout.tie(0);
#define error(args...)                           \
    {                                            \
        string _s = #args;                       \
        replace(_s.begin(), _s.end(), ',', ' '); \
        stringstream _ss(_s);                    \
        istream_iterator<string> _it(_ss);       \
        err(_it, args);                          \
    }
//NAMESPACES
using namespace __gnu_pbds;
using namespace std;
vector<string> vec_splitter(string s)
{
    s += ',';
    vector<string> res;
    while (!s.empty())
    {
        res.push_back(s.substr(0, s.find(',')));
        s = s.substr(s.find(',') + 1);
    }
    return res;
}
void debug_out(
    vector<string> __attribute__((unused)) args,
    __attribute__((unused)) int idx,
    __attribute__((unused)) int LINE_NUM) { cerr << endl; }
template <typename Head, typename... Tail>
void debug_out(vector<string> args, int idx, int LINE_NUM, Head H, Tail... T)
{
    if (idx > 0)
        cerr << ", ";
    else
        cerr << "Line(" << LINE_NUM << ") ";
    stringstream ss;
    ss << H;
    cerr << args[idx] << " = " << ss.str();
    debug_out(args, idx + 1, LINE_NUM, T...);
}
#ifdef XOX
#define debug(...) debug_out(vec_splitter(#__VA_ARGS__), 0, __LINE__, __VA_ARGS__)
#else
#define debug(...) 42
#endif
//HELPERS
int cnt(int n)
{
    int c = 0;
    while (n)
    {
        n /= 10;
        c++;
    }
    return c;
}
vector<int> powers2(32, 0);
void initialize()
{
    for (int i = 1; i < powers2.size(); i++)
        powers2[i] = powers2[i - 1] * 2;
}
int32_t main()
{
    IOS int n, m;
    cin >> n >> m;
    vector<pair<int, int>> res;
    FOR(i, 0, m)
    {
        int a, b;
        cin >> a >> b;
        res.push_back({a, b});
    }
    FOR(i, 0, 1000)
    {
        if (cnt(i) != n)
            continue;
        vector<int> t;
        int val = i;
        while (val)
        {
            t.push_back(val % 10);
            val /= 10;
        }
        reverse(all(t));
        int f = 1;
        FOR(i, 0, m)
        {
            if (t[res[i].first - 1] != res[i].second)
            {
                f = 0;
                break;
            }
        }
        if (f == 1)
        {
            cout << i;
            return 0;
        }
    }
    cout<<-1;
    return 0;
}
// Use emplace back in place of pushback
// Use tie function , for object destructuring