#include <algorithm>
#include <bits/stdc++.h>
#include <cstddef>
#include <cstdint>
#include <functional>
#include <iostream>
#include <iterator>
#include <type_traits>
#include <vector>

// lib/monoid.hpp
#ifndef MONOID_HPP
#define MONOID_HPP


namespace tools {
  template <typename T>
  class monoid {
  private:
    ::std::function<T(T, T)> m_operation;
    T m_identity;

  public:
    monoid(const ::std::function<T(T, T)>& operation, const T& identity) :
      m_operation(operation),
      m_identity(identity) {
    }
    monoid(const ::tools::monoid<T>&) = default;
    monoid(::tools::monoid<T>&&) = default;
    ::tools::monoid<T>& operator=(const ::tools::monoid<T>&) = default;
    ::tools::monoid<T>& operator=(::tools::monoid<T>&&) = default;
    virtual ~monoid() = default;

    T operation(const T& x, const T& y) const {
      return this->m_operation(x, y);
    }
    const T& identity() const {
      return this->m_identity;
    }

    template <typename U = T, typename ::std::enable_if<::std::is_integral<U>::value, ::std::nullptr_t>::type = nullptr>
    static ::tools::monoid<U> multiplies() {
      return ::tools::monoid<U>(::std::multiplies<U>(), 1);
    }
  };
}

#endif

// lib/util.hpp
#ifndef UTIL_HPP
#define UTIL_HPP


typedef ::std::int_fast64_t i64;
typedef ::std::uint_fast64_t u64;
typedef ::std::int_fast32_t i32;
typedef ::std::uint_fast32_t u32;

namespace tools {
  template <typename T>
  void read(::std::istream& is, ::std::vector<T>& vector, const typename ::std::vector<T>::size_type size) {
    vector.reserve(size);
    ::std::copy_n(::std::istream_iterator<T>(is), size, ::std::back_inserter(vector));
  }
  template <typename T>
  void read(::std::vector<T>& vector, const typename ::std::vector<T>::size_type size) {
    ::tools::read(::std::cin, vector, size);
  }

  template <typename T, ::std::size_t N>
  void read(::std::istream& is, ::std::array<T, N>& array) {
    ::std::copy_n(std::istream_iterator<T>(is), N, array.begin());
  }
  template <typename T, ::std::size_t N>
  void read(::std::array<T, N>& array) {
    ::tools::read(::std::cin, array);
  }
}

#endif

// lib/square.hpp
#ifndef SQUARE_HPP
#define SQUARE_HPP


/*
usage:

tools::square(5) => 25
*/

namespace tools {
  template <typename T>
  T square(const ::tools::monoid<T>& monoid, const T& x) {
    return monoid.operation(x, x);
  }

  template <typename T>
  T square(const T& x) {
    return ::tools::square(::tools::monoid<T>::multiplies(), x);
  }
}

#endif

// lib/pow.hpp
#ifndef POW_H
#define POW_H


/*
usage:

tools::pow(tools::monoid<int>::multiplies(), 2, 5) => 32
*/

namespace tools {
  template <typename T>
  T pow(const ::tools::monoid<T>& monoid, const T& base, const std::size_t exponent) {
    return exponent == 0
      ? monoid.identity()
      : exponent % 2 == 0
        ? ::tools::square(monoid, ::tools::pow(monoid, base, exponent / 2))
        : monoid.operation(::tools::pow(monoid, base, exponent - 1), base);
  }

  template <typename T>
  T pow(const T& base, const std::size_t exponent) {
    return ::tools::pow(::tools::monoid<T>::multiplies(), base, exponent);
  }
}

#endif

// main.cpp

int main() {
  i64 N, M;
  std::cin >> N >> M;
  std::vector<i64> s(M), c(M);
  for (i64 i = 0; i < M; ++i) {
    std::cin >> s[i] >> c[i];
  }

  for (i64 x = N == 1 ? 0 : tools::pow<i64>(10, N - 1); x < tools::pow<i64>(10, N); ++x) {
    for (i64 i = 0; i < M; ++i) {
      if (x / tools::pow<i64>(10, N - s[i]) % 10 != c[i]) {
        goto NEXT_CANDIDATE;
      }
    }

    std::cout << x << std::endl;
    return 0;

  NEXT_CANDIDATE:
    ;
  }

  std::cout << -1 << std::endl;
  return 0;
}

Measured memory_bytes: 256