package main
     
import "fmt"

 
func main() {
	var n, m int
    fmt.Scan(&n, &m)
    s := make([]int, m, m)
    c := make([]int, m, m)
    for i := 0; i < m; i++ {
        fmt.Scan(&s[i], &c[i])
    }
    num := make([]int, n, n)
    for i := range s {
        num[s[i]-1] = c[i]
    }
    
    if num[0] == 0 && len(num) > 1 {
        fmt.Println("-1")
        return 
    }
    ans := ""
    for _, v := range num {
        ans += fmt.Sprintf("%d", v)
    }
    fmt.Println(ans)
}