#include <bits/stdc++.h>
#include <iostream>
#include <algorithm>
#include <vector>
#include <tuple>
#define mod 1000000007
#define REP(i, n) for (int i = 0; i < (n); i++)
#define FOR(i, a, b) for (int i = (a); i <= (b); i++)
#define FORD(i, a, b) for (int i = (a); i >= (b); i--)
#define pb push_back
#define eb emplace_back
#define mp make_pair
#define mt make_tuple
#define debug(x) cout<<#x<<'='<<(x)<<endl;
#define debugp(x) cout<<#x<<"= {"<<(x.first)<<", "<<(x.second)<<"}"<<endl;
#define debug2(x, y) cout<<"{"<<#x<<", "<<#y<<"} = {"<<(x)<<", "<<(y)<<"}"<<endl;
#define debugv(v) cout<<#v<<" : ";for (auto x:v) cout<<x<<' ';cout<<endl;
#define all(x) x.begin(), x.end()
inline bool EQ(double a, double b) { return fabs(a - b) < 1e-9; }
const int INF = 1 << 29;
typedef long long ll;
typedef unsigned long long ull;
inline int two(int n) { return 1 << n; }
inline int test(int n, int b) { return (n >> b) & 1; }
inline void set_bit(int &n, int b) { n |= two(b); }
inline void unset_bit(int &n, int b) { n &= ~two(b); }
inline int last_bit(int n) { return n & (-n); }
inline int ones(int n)
{
    int res = 0;
    while (n && ++res)
        n -= n & (-n);
    return res;
}
template <class T>
void chmax(T &a, const T &b) { a = max(a, b); }
template <class T>
void chmin(T &a, const T &b) { a = min(a, b); }

long long int gcd(long long int a, long long int b)
{
    if (b == 0)
        return a;
    return gcd(b, a % b);
}

long long int lcm(long long int a, long long int b)
{
    return (a * b) / gcd(a, b);
}

long long int max(long long int a, long long int b)
{
    if (a > b)
        return a;
    return b;
}

long long int power(long long int x, long long int y)
{
    long long int res = 1;
    while (y > 0)
    {
        if (y & 1)
            res = res * x;
        y = y >> 1;
        x = x * x;
    }
    return res;
}

long long int powermod(long long int x, long long int y)
{
    long long int res = 1;
    x = x % mod;
    while (y > 0)
    {
        if (y & 1)
            res = (res * x) % mod;
        y = y >> 1;
        x = (x * x) % mod;
    }
    return res;
}

long long mulmod(long long a, long long b)
{
    long long res = 0;
    a %= mod;
    while (b)
    {
        if (b & 1)
            res = (res + a) % mod;
        a = (2 * a) % mod;
        b >>= 1;
    }

    return res;
}

bool isPrime(long long int n)
{
    if (n <= 1)
        return false;
    if (n <= 3)
        return true;
    if (n % 2 == 0 || n % 3 == 0)
        return false;
    for (int i = 5; i * i <= n; i += 6)
    {
        if ((n % i == 0) || (n % (i + 2) == 0))
            return false;
    }
    return true;
}

long double dist(long long int x1, long long int y1, long long int x2, long long int y2)
{
    return (long double)sqrt((long double)((x1 - x2) * (x1 - x2) + (y1 - y2) * (y1 - y2)));
}
long long int squaredist(long long int x1, long long int y1, long long int x2, long long int y2)
{
    return ((x1 - x2) * (x1 - x2) + (y1 - y2) * (y1 - y2));
}

long long int nCr(long long int n, long long int r)
{
    if (r == 0)
        return 1;
    return (n * nCr(n - 1, r - 1)) / r;
}

long long int countDivisors(long long int n)
{
    long long int cnt = 0;
    for (int i = 1; i <= sqrt(n); i++)
    {
        if (n % i == 0)
        {
            if (n / i == i)
                cnt++;
            else
                cnt = cnt + 2;
        }
    }
    return cnt;
}

unsigned long long int countDivisibles(unsigned long long int A,unsigned long long int B,unsigned long long int M)
{
    if (A % M == 0)
        return (B / M) - (A / M) + 1;

    return (B / M) - (A / M);
}

long long int xorRange(long long int x, long long int y)
{
    if (x % 2 == 0)
    {
        long long int pattern[] = {y, 1, y + 1, 0};
        return pattern[(int)((y - x) % 4)];
    }
    else
    {
        long long int pattern[] = {x, x ^ y, x - 1, (x - 1) ^ y};
        return pattern[(int)((y - x) % 4)];
    }
}

unsigned long long int maxOrRange(unsigned long long int l,unsigned long long int r)
{
     while(l < r) l &= (l+1);
     return (l & r); 
}

long long mul(long long a,long long b){
    return (a*b)%mod;
}

long long mul(long a,long long b,long long c){
    return mul(mul(a,b),c);
}

long long mul(long long a,long long b,long long c,long long d){
    return mul(mul(a,b),mul(c,d));
}

long long add(long long a,long long b){
    return (a+b)%mod;
}

long long neg(long long a){
    return (mod-(a%mod))%mod;
}

long long sub(long long a,long long b){
    return add(a,neg(b));
}

long long minv(long long a){
    int b=mod-2;
    long long ans=1;
    while(b){
        if(b%2)
            ans=mul(ans,a);
        a=mul(a,a);
        b/=2;
    }
    return ans;
}

long long divi(long long a,long long b){
    return mul(a,minv(b));
}

bool sortdesc(const std::tuple<int, int, int>& a, const std::tuple<int, int, int>& b) 
{ 
    return (std::get<0>(a) > std::get<0>(b)); 
} 

std::vector<long long> fni(100000); 
std::vector<long long> nni (100000); 
std::vector<long long> fact(100000); 

void Inv_Num_Fact_Factorial(long long p,long long N){
     fni[0] = fni[1] = nni[0] = nni[1] = fact[0] = 1;
     for(int i=1;i<=N;i++){
        if(i>=2) {
            nni[i] = mul(nni[p % i],(p - p / i));
            fni[i] = mul(nni[i],fni[i - 1]); 
        }
        fact[i] = mul(fact[i - 1] ,i); 
     }
}

long long fnCr(long long int N,long long int R) 
{ 
    return mul(fact[N],fni[R],fni[N - R]); 
} 

using namespace std;

long long powerr(long long x, long long y, long long m) 
{ 
    if (y == 0) 
        return 1; 
    ll p = powerr(x, y/2, m) % m; 
    p = (p * p) % m; 
  
    return (y%2 == 0)? p : (x * p) % m; 
} 

ll modInverse(long long a,long long m) 
{  
    return powerr(a, m-2, m); 
} 

ll andd(ll a,ll b){
    while(a<b){
            b -= (b & -b);
           // cout << b << "\n";
    }
    return b%mod;
}

ull highestPowerof2(ll n) 
{ 
   ull p = (ull)log2(n); 
   return (ull)pow(2, p);  
}   

int main()
{
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);
    

    int n,m;
    cin >> n >> m;
    int arr[n] = {0};
    for(int i=0;i<m;i++){
        int a,b;

        cin >> a >> b;
        arr[a-1] = b;
    }
    if(m<n) cout << -1;
    else{
        string s;
        for(int i=0;i<n;i++){
            s += to_string(arr[i]);
        }
        cout << stoi(s);
    }
    return 0;
}