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 <cstdio>

int ans[5];

int N,M;
int request[10][2];

int main(){
    scanf("%d%d",&N,&M);
    if (N>1)
        ans[N]=1;

    for(int i=1;i<=M;i++){
        int s,c;
        scanf("%d%d",&s,&c);
        request[i][0]=s;
        request[i][1]=c;
        ans[N+1-s]=c;
    }

    bool ok=(ans[N]!=0)||N==1;
    for(int i=1;i<=M;i++)
        ok=ok&&(ans[N+1-request[i][0]]==request[i][1]);

    if (ok){
        for(int i=N;i>=1;i--) printf("%d",ans[i]);
        putchar('\n');
    }else puts("-1");


    return 0;
}