#include <bits/stdc++.h>
using namespace std;
 
#define ull     		unsigned long long int
#define ll      		long long int
#define loop(i,s,e)     for(ll i=(s);i<(e);i++)
#define rloop(i,s,e)    for(ll i=(s);i>=(e);i--)
#define scan(any)       for(auto &i:any) cin>>i;
#define print(any)      for(auto i:any) cout<<i<<" "; nl;
#define nl              cout<<'\n'
#define pi 3.141592654
#define hell 1000000007
#define io ios_base::sync_with_stdio(false);cin.tie(0);cout.tie(0)
#define fix(n) cout << fixed << setprecision(n)
#define IP(n) int n;cin>>n
#define IP2(a, b) int a,b;cin>>a>>b
#define Max(a,b) ((a)>(b)?(a):(b))
#define Min(a,b) ((a)<(b)?(a):(b))
#define rep(i,a,b) for (__typeof((b)) i=(a);i<(b);i++)
#define ren(i,a,b) for(__typeof((a)) i=(a);i>=(b);i--)
#define mp make_pair
#define pb push_back
#define fi first
#define se second
#define vi vector<int>
#define pii pair<int,int>
#define piii pair<pair<int,int>,int>
#define all(v) (v).begin(), (v).end()
#define sz(x) (int)x.size()
#define set(a,n) memset(a,n,sizeof(a))
#define DEBUG(x) cout << '>' << #x << ':' << x << endl;
const int INF = 1<<29;
inline int two(int n) { return 1 << n; }
inline int last_bit(int n) { return n & (-n); }
inline int test(int n, int b) { return (n>>b)&1; }
inline bool EQ(double a, double b) { return fabs(a-b) < 1e-9; }
inline void unset_bit(int & n, int b) { n &= ~two(b); }
inline void set_bit(int & n, int b) { n |= two(b); }
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); }
/////////////////////////////////////////////////////////////////////////////////
int main()
{
IP2(n,m);
vi s(m);
vi c(m);
int ans1=10,ans2=10,ans3=10;
loop(i,0,m){
cin>>s[i];
cin>>c[i];
if(s[i]==1 && c[i]!=0)
chmin(ans1,c[i]);
if(s[i]==2)
chmin(ans2,c[i]);
if(s[i]==3)
chmin(ans3,c[i]);
if(m==1 && n==1 && c[i]==0)
ans=0;
}
if(ans1==10)
cout<<-1;
else
{
cout<<ans1;
if(ans2==10)
ans2=0;
if(ans3==10)
ans3=0;
if(n>=2)
cout<<ans2;
if(n==3)
cout<<ans3;
}

return 0;
}	
