#include <fstream>
#include <iostream>
#include <functional>
#include <algorithm>
#include <sstream>
#include <cstring>
#include <vector>
#include <string>
#include <cstdio>
#include <cmath>
#include <queue>
#include <stack>
#include <deque>
#include <ctime>
#include <list>
#include <set>
#include <map>
#include <bitset>
#include <iomanip>

using namespace std;
 
typedef long long ll;
typedef unsigned long long ull;
#define SORT_UNIQUE(c) (sort(c.begin(),c.end()), c.resize(distance(c.begin(),unique(c.begin(),c.end()))))
#define GET_POS(c,x) (lower_bound(c.begin(),c.end(),x)-c.begin())
#define CASET int ___T; scanf("%d", &___T); for(int cs=1;cs<=___T;cs++)
#define MS0(X) memset((X), 0, sizeof((X)))
#define MS1(X) memset((X), -1, sizeof((X)))
#define EPS 1e-8
#define LL_INF 0x3fffffffffffffff
#define INF 0x3f3f3f3f3f3f3f3f
#define MEM(a, b) memset(a, b, sizeof(a))
#define PPER(i, n, m) for (int i = n; i >= m; i--)
#define REPP(i, n, m) for (int i = n; i <= m; i++)
#define REP(i, n, m) for (int i = n; i < m; i++)
#define PER(i, n, m) for (int i = n; i > m; i--)
#define SA(n) scanf("%d", &(n))
#define SLLA(n) scanf("%lld", &(n))
#define MP make_pair
#define FF first
#define SS second
#define PB push_back
#define DE(val) cout << #val << ": " << val << endl;
 
const int dx44[6] = {0, -1, -1, 1, 1};
const int dy44[6] = {0, -1, 1, -1, 1};
const int dx4[6] = {0, 0, 1,-1};
const int dy4[6] = {1, -1, 0,0};
const int dx8[9] = {0, -1, 0, 1, 0, 1, 1, -1, -1};
const int dy8[9] = {0, 0, 1, 0, -1, 1, -1, 1, -1};
const int dx82[9] = {0, -1, -1, 1, 1, 2, 2, -2, -2};
const int dy82[9] = {0, 2, -2, 2, -2, 1, -1, 1, -1};

void update(ll& x,ll v){
    if(x==-1)x=v;
    else if(x>v)x=v;
}
 
ll po(ll a, ll b, ll mod)
{
    ll res = 1;
    a %= mod;
    for (; b; b >>= 1)
    {
        if (b & 1)
            res = res * a % mod;
        a = a * a % mod;
    }
    return res;
}
ll gcd(ll a, ll b)
{
    if (a == 0)
    {
        return b;
    }
    else
    {
        return gcd(b % a, a);
    }
}
void extgcd(ll a, ll b, ll &d, ll &x, ll &y)
{
    if (!b)
    {
        d = a;
        x = 1;
    }
    else
    {
        extgcd(b, a % b, d, y, x);
        y -= x * (a / b);
    }
}
ll inverse(ll a, ll n)
{
    ll d, x, y;
    extgcd(a, n, d, x, y);
    return d == 1 ? (x + n) % n : -1;
}
#define SORT_UNIQUE(c) (sort(c.begin(),c.end()), c.resize(distance(c.begin(),unique(c.begin(),c.end()))))
const int maxn = 5e5 + 15;
const double PI = acos(-1.0);
const ll mod = 1e9 + 7;
/*************************************************************************/

int val[15][15];
void solve() {
   int n,m;
   SA(n);
   SA(m);
   map<int,int> hax;
   REPP(i,1,m) {
    int x,y;
    SA(x),SA(y);
    if(hax.count(x) && hax[x] != y) {
        puts("-1");
        return;
    }
    if(x == 1 && y == 0) {
        if(n != 1) {
            puts("-1");
            return;
        }
    }
    if(x > n) {
        puts("-1");
        return;
    }
    hax[x] = y;
   }
   REPP(i,0,999) {
    int x = i;
    int cnt = 0;
    std::vector<int> v;
    if(x == 0) {
        v.push_back(0);
    } else {
        while(x > 0) {
            v.push_back(x%10);
            x/=10;
        }
    }
    if(v.size() != n) {
        continue;
    }
    reverse(v.begin(), v.end());
    int flag = 1;
    
    REP(k,0,v.size()) {
        if(!hax.count(k+1)) {
            continue;
        }
        if(v[k] != hax[k+1]) {
            flag = 0;
            continue;
        }
    }
    if(flag) {
        cout<<i<<endl;
        return;
    }
   }
   cout<<-1<<endl;
}

int main()
{   
// #ifndef ONLINE_JUDGE
//     freopen("i.txt", "r", stdin);
//      freopen("o.txt", "w", stdout);
// #endif
   solve();
    return 0;
 
}
 

Measured memory_bytes: 384