#include <bits/stdc++.h>

using namespace std;
typedef long long ll;
typedef pair<ll, ll> p_ll;

template<class T>
void debug(T itr1, T itr2) { auto now = itr1; while(now<itr2) { cout << *now << " "; now++; } cout << endl; }
#define repr(i,from,to) for (int i=(int)from; i<(int)to; i++)
#define all(vec) vec.begin(), vec.end()
#define rep(i,N) repr(i,0,N)
#define per(i,N) for (int i=(int)N-1; i>=0; i--)

const ll MOD = pow(10,9)+7;
const ll LLINF = pow(2,61)-1;
const int INF = pow(2,30)-1;

vector<ll> fac;
void c_fac(int x=pow(10,6)+10) { fac.resize(x,true); rep(i,x) fac[i] = i ? (fac[i-1]*i)%MOD : 1; }
ll inv(ll a, ll m=MOD) { ll b = m, x = 1, y = 0; while (b!=0) { int d = a/b; a -= b*d; swap(a,b); x -= y*d; swap(x,y); } return (x+m)%m; }
ll nck(ll n, ll k) { return fac[n]*inv(fac[k]*fac[n-k]%MOD)%MOD; }
ll gcd(ll a, ll b) { if (a<b) swap(a,b); return b==0 ? a : gcd(b, a%b); }
ll lcm(ll a, ll b) { return a/gcd(a,b)*b; }


int main() {
  int N, M; cin >> N >> M;
  int s[M], c[M]; rep(i,M) { cin >> s[i] >> c[i]; s[i]--; }
  int result = -1;
  int b[3] = {0,10,100}, e[3] = {9,99,999};
  repr(i,b[N-1],e[N-1]) {
    int tmp = i, n[N] = {};
    rep(j,N) { n[j] = tmp%10; tmp /= 10; }
    reverse(n,n+N);
    bool ok = true;
    rep(i,M) if (n[s[i]]!=c[i]) ok = false;
    if (ok) { result = i; break; }
  }
  cout << result << endl;
  return 0;
}