import std.conv, std.functional, std.range, std.stdio, std.string;
import std.algorithm, std.array, std.bigint, std.bitmanip, std.complex, std.container, std.math, std.mathspecial, std.numeric, std.regex, std.typecons;
import core.bitop;

class EOFException : Throwable { this() { super("EOF"); } }
string[] tokens;
string readToken() { for (; tokens.empty; ) { if (stdin.eof) { throw new EOFException; } tokens = readln.split; } auto token = tokens.front; tokens.popFront; return token; }
int readInt() { return readToken.to!int; }
long readLong() { return readToken.to!long; }
real readReal() { return readToken.to!real; }

bool chmin(T)(ref T t, in T f) { if (t > f) { t = f; return true; } else { return false; } }
bool chmax(T)(ref T t, in T f) { if (t < f) { t = f; return true; } else { return false; } }

int binarySearch(alias pred, T)(in T[] as) { int lo = -1, hi = cast(int)(as.length); for (; lo + 1 < hi; ) { const mid = (lo + hi) >> 1; (unaryFun!pred(as[mid]) ? hi : lo) = mid; } return hi; }
int lowerBound(T)(in T[] as, T val) { return as.binarySearch!(a => (a >= val)); }
int upperBound(T)(in T[] as, T val) { return as.binarySearch!(a => (a > val)); }


enum LIM = 10^^5 + 10;

void main() {
  try {
    for (; ; ) {
      const N = readInt;
      const M = readInt;
      auto B = new int[M];
      auto C = new int[M];
      foreach (i; 0 .. M) {
        B[i] = readInt;
        C[i] = readInt;
        if ((C[i] %= B[i]) < 0) C[i] += B[i];
      }
      debug {
        writeln("B = ", B);
        writeln("C = ", C);
      }
      
      bool good = true;
      auto cs = new int[LIM];
      cs[] = -1;
      foreach (i; 0 .. M) {
        if (!~cs[B[i]]) {
          cs[B[i]] = C[i];
        }
        good = good && (cs[B[i]] == C[i]);
      }
      debug {
        writeln("good = ", good);
        writeln("cs = ", cs[0 .. 11]);
      }
      if (good) {
        int cnt;
        auto fs = new int[N + 1];
        foreach (b; 1 .. LIM) if (~cs[b]) {
          ++cnt;
          for (int x = cs[b]; x <= N; x += b) {
            ++fs[x];
          }
        }
        foreach (x; 0 .. N + 1) {
          if (cnt == fs[x]) {
            writeln(x);
            goto found;
          }
        }
      }
      writeln("NaN");
     found:
    }
  } catch (EOFException e) {
  }
}