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>
#define LL long long
using namespace std;
const int maxn = 1e5+5;

int n, m, a[10];
int main(){
    cin >> n >> m;

    memset(a, -1, sizeof a);
    int x, y, f=1;
    while(m--){
        cin >> x >> y;
        if(a[x] != -1 && a[x] != y) f = 0;
        else a[x] = y;
    }
    if(f==0 || (n>1 && a[1]==0)) puts("-1");
    else {
        if(n>1 && a[1]==-1) a[1] = 1;
        for(int i=1; i<=n; i++) cout << max(0,a[i]); cout << endl;
    }
}