#include <bits/stdc++.h>
using namespace std;
#define repr(i,a,b) for(int i=a;i<b;i++)
#define rep(i,n) for(int i=0;i<n;i++)
#define reprrev(i,a,b) for(int i=b-1;i>=a;i--) // [a, b)
#define reprev(i,n) reprrev(i,0,n)
typedef long long ll;
typedef unsigned long long ull;
template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return true; } return false; }
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return true; } return false; }

/* attention
    long longのシフト演算には気をつけよう
    タイポした時のデバッグが死ぬほどきつくなるので変数名は最低3字くらい使った方がいいかも
*/

const ll mod = 1e9+7;

void chmod(ll &M){
    if(M >= mod) M %= mod;
    else if(M < 0){
        M += (abs(M)/mod + 1)*mod;
        M %= mod;
    }
}

ll modpow(ll x, ll n){
    if(n==0) return 1;
    ll res=modpow(x, n/2);

    if(n%2==0) return res*res%mod;
    else return res*res%mod*x%mod;
}

int getl(int i, int N) { return i==0? N-1:i-1; };
int getr(int i, int N) { return i==N-1? 0:i+1; };


// 線分 ab の偏角 返り値は[-π, π]
double argument(const pair<double, double> &a, const pair<double, double> &b){
    double ax=a.first, ay=a.second, bx=b.first, by=b.second;
    return atan2(by-ay, bx-ax);
}

/* <-----------------------------------------------------------------------------------> */
/* <-----------------------------------------------------------------------------------> */
/* <-----------------------------------------------------------------------------------> */
/* <-----------------------------------------------------------------------------------> */



int main(){
    cin.tie(nullptr);
    ios::sync_with_stdio(false);

    int n, m; cin >> n >> m;
    string ans(n, '-');

    if(n == 1) {
        rep(i, m) {
            int j, c; cin >> j >> c;
            j--;
            if(ans[j] != '-' && ans[j] != c+'0') { cout << -1 << endl; return 0; }
            ans[j] = c+'0';
        }
        if(ans == '-') cout << 0 << endl;
        else cout << ans << endl;
        return 0;
    } 

    rep(i, m) {
        int j, c; cin >> j >> c;
        j--;
        if(j==0 && c==0) { cout << -1 << endl; return 0; }
        if(ans[j] != '-' && ans[j] != c+'0') { cout << -1 << endl; return 0; }
        ans[j] = c+'0';
    }

    rep(i, n) if(ans[i]=='-') {
        if(i==0) ans[i] = '1';
        else ans[i] = '0';
    }

    cout << ans << endl;
    
    return 0;
}