If there is an integer not less than 0 satisfying the following conditions, print the smallest such integer; otherwise, print `-1`.

* The integer has exactly N digits in base ten. (We assume 0 to be a 1-digit integer. For other integers, leading zeros are not allowed.)
* The s_i-th digit from the left is c_i. \left(i = 1, 2, \cdots, M\right)

Constraints

* All values in input are integers.
* 1 \leq N \leq 3
* 0 \leq M \leq 5
* 1 \leq s_i \leq N
* 0 \leq c_i \leq 9

Input

Input is given from Standard Input in the following format:


N M
s_1 c_1
\vdots
s_M c_M


Output

Print the answer.

Examples

Input

3 3
1 7
3 2
1 7


Output

702


Input

3 2
2 1
2 3


Output

-1


Input

3 1
1 0


Output

-1
#include <bits/stdc++.h>
using namespace std;

int main(){
    cin.tie(0);
    ios::sync_with_stdio(false);
    int N,M; cin >> N >> M;
    vector<int> s(M);
    vector<char> c(M);
    for (int i=0;i<M;++i) cin >> s[i] >> c[i];
    for (int i=0;i<1000;++i){
        string S=to_string(i);
        if (S.size()!=N) continue;
        int ok=1;
        for (int j=0;j<M;++j)
            if (S[s[j]-1]!=c[j]) ok=0;
        if (ok){
            cout << i << '\n';
            return 0;
        }
    }
    cout << -1 << '\n';
}
