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
// C - Guess The Number
#include <bits/stdc++.h>
using namespace std;
#define rep(i,n) for(int i=0;i<(n);++i)

int main(){
	int N,M; cin>>N>>M;
	int S[M]; char C[M];
	rep(i,M){ cin>>S[i]>>C[i]; --S[i]; }
	int ans = 1000;
	rep(i,1000){
		string A = to_string(i);
		if(A.size() != N) continue;
		bool ok = true;
		rep(j,M) if(A[S[j]] != C[j]){ ok = false; break; }
		if(ok){ cout<<i<<endl; return 0; }
	}
	puts("-1");
}