#include <bits/stdc++.h>
class IO {
  static const int bufSize = 1 << 18;
  char inBuf[bufSize], outBuf[bufSize];
  char *ip1 = inBuf, *ip2 = inBuf;
  int goodReadBit = 0, op1 = -1, op2 = bufSize - 1;
  template <typename T>
  __inline__ __attribute__((always_inline)) void __RI(T& x) {
    int ch = gc(), neg = 1;
    x = 0;
    for (; !(isdigit(ch) || ch == '-' || ch == EOF); ch = gc())
      ;
    if (ch == EOF) {
      goodReadBit = 0;
      return;
    }
    if (ch == '-') neg = -1, ch = gc();
    for (; isdigit(ch); ch = gc()) x = x * 10 + (ch - 48) * neg;
  }
  template <typename T>
  __inline__ __attribute__((always_inline)) void __RC(T& x) {
    unsigned char ch;
    while (isspace(ch = gc()))
      ;
    x = ch;
  }
  __inline__ __attribute__((always_inline)) void __RS(std::string& x) {
    char ch;
    x.clear();
    for (ch = gc(); isspace(ch); ch = gc())
      ;
    if (ch == EOF) {
      goodReadBit = 0;
      return;
    }
    for (; !isspace(ch); ch = gc()) x.push_back(ch);
  }

 public:
  __inline__ __attribute__((always_inline)) int gc() {
    return ip1 == ip2 && (ip2 = (ip1 = inBuf) + fread(inBuf, 1, bufSize, stdin),
                          ip1 == ip2)
               ? EOF
               : *ip1++;
  }
  __inline__ __attribute__((always_inline)) void R(char& x) { __RC(x); }
  __inline__ __attribute__((always_inline)) void R(unsigned char& x) {
    __RC(x);
  }
  __inline__ __attribute__((always_inline)) void R(std::string& x) { __RS(x); }
  template <typename T1, typename T2>
  __inline__ __attribute__((always_inline)) void R(std::pair<T1, T2>& x) {
    R(x.first), R(x.second);
  }
  template <typename T>
  __inline__ __attribute__((always_inline)) void R(std::vector<T>& x) {
    for (auto it = x.begin(); it != x.end(); ++it) R(*it);
  }
  template <typename T, typename... Args>
  __inline__ __attribute__((always_inline)) void RA(T* a, int n) {
    for (int i = 0; i < n; ++i) R(a[i]);
  }
  template <typename T, typename... Args>
  __inline__ __attribute__((always_inline)) void R(T& x, Args&... args) {
    R(x), R(args...);
  }
  template <typename T, typename... Args>
  __inline__ __attribute__((always_inline)) void RA(T* a, int n, Args... args) {
    for (int i = 0; i < n; ++i) RA(a[i], args...);
  }
  template <typename T>
  __inline__ __attribute__((always_inline)) void R(T& x) {
    static_assert(std::is_integral<T>::value, "Unsupported types");
    if (std::is_integral<T>::value) __RI(x);
  }

 private:
  char space;
  template <typename T>
  __inline__ __attribute__((always_inline)) void __WI(T x) {
    static char buf[64];
    static int len = -1;
    if (x >= 0) {
      do {
        buf[++len] = x % 10 + 48, x /= 10;
      } while (x);
    } else {
      pc('-');
      do {
        buf[++len] = -(x % 10) + 48, x /= 10;
      } while (x);
    }
    while (len >= 0) {
      pc(buf[len]), --len;
    }
  }

 public:
  __inline__ __attribute__((always_inline)) void pc(const char& x) {
    if (op1 == op2) flush();
    outBuf[++op1] = x;
  }
  __inline__ __attribute__((always_inline)) void flush() {
    fwrite(outBuf, 1, op1 + 1, stdout), op1 = -1;
  }
  __inline__ __attribute__((always_inline)) void W(const char& x) { pc(x); }
  __inline__ __attribute__((always_inline)) void W(const char* x) {
    while (*x != '\0') pc(*(x++));
  }
  __inline__ __attribute__((always_inline)) void W(const std::string& x) {
    W(x.c_str());
  }
  template <typename T>
  __inline__ __attribute__((always_inline)) void W(const std::vector<T>& x) {
    for (auto it = x.begin(); it != x.end(); it++) WS(*it);
    WL();
  }
  __inline__ __attribute__((always_inline)) void WL() { W('\n'); }
  template <typename T>
  __inline__ __attribute__((always_inline)) void WL(const T& x) {
    W(x), W('\n');
  }
  __inline__ __attribute__((always_inline)) void WS() { W(' '); }
  template <typename T>
  __inline__ __attribute__((always_inline)) void WS(const T& x) {
    W(x), W(space);
  }
  template <typename T>
  __inline__ __attribute__((always_inline)) void WA(T* a, int n) {
    for (int i = 0; i < n; i++) WS(a[i]);
    WL();
  }
  template <typename T, typename... Args>
  __inline__ __attribute__((always_inline)) void W(const T& x,
                                                   const Args&... args) {
    W(x), W(space), W(args...);
  }
  template <typename... Args>
  __inline__ __attribute__((always_inline)) void WL(const Args&... args) {
    W(args...), W('\n');
  }
  template <typename T, typename... Args>
  __inline__ __attribute__((always_inline)) void WA(T* a, int n, Args... args) {
    for (int i = 0; i < n; i++) WA(a[i], args...);
  }
  template <typename T>
  __inline__ __attribute__((always_inline)) void W(const T& x) {
    static_assert(std::is_integral<T>::value, "Unsupported types");
    if (std::is_integral<T>::value) __WI(x);
  }
  template <typename T>
  __inline__ __attribute__((always_inline)) IO& operator>>(T& x) {
    R(x);
    return (*this);
  }
  template <typename T>
  __inline__ __attribute__((always_inline)) IO& operator<<(const T& x) {
    W(x);
    return (*this);
  }
  IO() { space = ' '; }
} io;
namespace Alphagocc {
decltype(std::chrono::high_resolution_clock::now()) tStart;
};
void TimeBegin() {
  Alphagocc::tStart = std::chrono::high_resolution_clock::now();
}
long long TimeEnd() {
  return (std::chrono::high_resolution_clock::now() - Alphagocc::tStart)
      .count();
}
using namespace std;
const int8_t INFC = 0x3f;
const int16_t INFS = 0x3f3f;
const int32_t INF = 0x3f3f3f3f;
const int64_t INFL = 0x3f3f3f3f3f3f3f3fLL;
namespace Alphagocc {
int MAIN() {
  int n, m;
  io >> n >> m;
  string ans(n, '*');
  bool flg = 1;
  for (int i = 0; i < m; i++) {
    int s, c;
    io >> s >> c;
    if (ans[s - 1] != c + 48 && ans[s - 1] != '*') {
      flg = 0;
      break;
    } else
      ans[s - 1] = c + 48;
  }
  for (int i = 0; i < n; i++)
    if (ans[i] == '*') ans[i] = '0';
  if (flg && (n == 1 || ans[0] != '0'))
    io.WL(ans);
  else
    io.WL(-1);
  io.flush();
  return 0;
}
}  // namespace Alphagocc
int main() { return Alphagocc::MAIN(); }
