#pragma GCC optimize("O3", "unroll-loops")
//#pragma GCC target("avx2")
#include <bits/stdc++.h>
#include <stdio.h>

using namespace std;
#define ull unsigned long long
#define si short int
#define ll long long
#define ld long double
#define pb push_back
#define pii pair<int, int>
#define pil pair<int, ll>
#define pli pair<ll, int>
#define pll pair<ll, ll>
#define piii pair<pair<int, int>, int>
#define all(vec) vec.begin(), vec.end()
#define piiii pair<pair<int, int>, pair<int, int>>
#define fr(a, from, c) for(int a=(from); (a)<(c); (a)++)

/*-----------------------------------------------------SegTree---------------------------------------------*/
int mxn11 = (int)(5e5 + 1);
vector<vector<int>> t(26, vector<int>(4*mxn11));
string s;
void build(int v, int vl, int vr, int i) {
    if (vl == vr) {
        if(s[vl]-'a' == i){
            t[i][v]=1;
        }
    } else {
        int tmp = (vl + vr) >> 1;
        build(2 * v, vl, tmp, i);
        build(2 * v + 1, tmp + 1, vr, i);
        t[i][v]=t[i][2*v] + t[i][2*v+1];
    }
}


int get(int v, int vl, int vr, int l, int r, int i) {
    if (l > r) return 0;
    if (vl == l && vr == r) {
        return t[i][v];
    }
    int tmp = (vl + vr) >> 1;
    ll a = get(2 * v, vl, tmp, l, min(tmp, r), i);
    ll b = get(2 * v + 1, tmp + 1, vr, max(tmp + 1, l), r, i);
    return a+b;
}

void update(int v, int vl, int vr, int pos, int what) {
    if(vl==vr){
        for(int i=0;i<26;i++){
            t[i][v]=(what==i)? 1:0;
        }
        return;
    }
    int tmp=(vl+vr)>>1;
    if(pos<=tmp)
        update(2*v, vl, tmp, pos, what);
    else
        update(2*v+1, tmp+1, vr, pos, what);
    for(int i=0;i<26;i++){
        t[i][v]=t[i][2*v+1]+t[i][2*v];
    }
}
/*-----------------------------------------------------SegTree---------------------------------------------*/

/*-----------------------------------------------------MATH------------------------------------------------*/
inline ll gcd(ll a, ll b) {
    while (b) {
        a %= b;
        swap(a, b);
    }
    return a;
}

inline ll lcm(ll a, ll b) { return a / gcd(a, b) * b; }

inline ll pwm(ll xx, ll pow, ll MD) {
    if (pow < 0) { pow = pow % (MD - 1) + MD - 1; }
    ll mlt = 1;
    while (pow) {
        if (pow & 1) {
            mlt *= xx;
            mlt %= MD;
        }
        xx *= xx;
        pow >>= 1;
        xx %= MD;
    }
    return mlt;
}
inline ll gcdex(ll a, ll b, ll &x, ll &y) {
    if (b == 0) {
        x = 1;
        y = 0;
        return a;
    }
    ll xx, yy;
    ll gc = gcdex(b, a % b, yy, xx);
    x = xx;
    y = yy - (a / b) * xx;
    return gc;
}

inline int inv(ll r, int _mod) { return pwm(r % _mod, _mod - 2, _mod); }

inline int64_t hilbertOrder(int x, int y, int pow, int rotate) {
    if (pow == 0) {
        return 0;
    }
    int hpow = 1 << (pow - 1);
    int seg = (x < hpow) ? (
            (y < hpow) ? 0 : 3
    ) : (
                      (y < hpow) ? 1 : 2
              );
    seg = (seg + rotate) & 3;
    const int rotateDelta[4] = {3, 0, 0, 1};
    int nx = x & (x ^ hpow), ny = y & (y ^ hpow);
    int nrot = (rotate + rotateDelta[seg]) & 3;
    int64_t subSquareSize = int64_t(1) << (2 * pow - 2);
    int64_t ans = seg * subSquareSize;
    int64_t add = hilbertOrder(nx, ny, pow - 1, nrot);
    ans += (seg == 1 || seg == 2) ? add : (subSquareSize - add - 1);
    return ans;
}

/*-----------------------------------------------------MATH------------------------------------------------*/
vector<vector<int>> vert(1e5+1, vector<int>());
vector<vector<int>> block(1e5+1, vector<int>());
vector<bool> was(1e5+1, false);
vector<int> components(1e5+1, -1);
vector<int> vectpush;
vector<int> ans(1e5+1, 0);
int kolvo;
void dfs(int v, int c){
    was[v]=true;
    vectpush.pb(v);
    components[v]=c;
    kolvo++;
    for(int son:vert[v]){
        if(was[son]) continue;
        dfs(son, c);
    }
}
int gettt(int num, int c){
    while(c--){
        num/=10;
    }
    return num%10;
}

void solve() {
   int n,m;
   cin>>n>>m;
   vector<pii> arr(m);
   for(int i=0;i<m;i++){
        cin>>arr[i].first>>arr[i].second;
   }
   for(int i=0;i<pwm(10, n, 10000);i++){
       int digits=0;
       int tmp=i;
       do{
           tmp/=10;
           digits++;
       } while(tmp!=0);
       if(digits!=n) continue;
       bool ok=true;
       for(int j=0;j<m;j++){
           if(gettt(i,n-arr[j].first)!=arr[j].second){
               ok=false;
           }
       }
       if(ok){
           cout<<i<<endl;
           return;
       }
   }
   cout<<-1;

}

int main() {
    /*ios::sync_with_stdio(false);
    cin.tie(nullptr);*/
    //freopen("C:\\Users\\Maximus\\CLionProjects\\Codeforces\\BestTeam\\output.txt", "r", stdin);
    //freopen("C:\\Users\\Maximus\\CLionProjects\\Codeforces\\BestTeam\\output.txt", "w", stdout);
    //unsigned int beg_time = clock();
    int n = 1;
    for (int i = 0; i < n; i++) solve();


    //unsigned int end_time = clock();
    //cout<<endl<<endl<<end_time-beg_time;

    return 0;
}

Measured memory_bytes: 211328