#include<bits/stdc++.h> 
#define N 110

using namespace std;

typedef long long ll;

struct rec
{
	int k,f;
};

rec a[N];

int main()
{
	ios::sync_with_stdio(false);
    cin.tie(0);
    int n,m;
	cin >> n >> m;
	for (int i=1;i<=m;i++)
		cin >> a[i].k >> a[i].f;
	for (int i=1;i<=m;i++)
	{
		for (int j=1;j<=m;j++)
		{
			if (a[j].f+1==a[i].f && a[j].k+1==a[i].k)
			{
				int l = a[j].k/a[j].f;
				if (n%l==0) cout << n/l << endl;
				else cout << n/l+1 << endl;
				return 0;
			}
			if (a[j].f-1==a[i].f && a[j].k-1==a[i].k)
			{
				int l = a[i].k/a[i].f;
				if (n%l==0) cout << n/l << endl;
				else cout << n/l+1 << endl;
				return 0;
			}
		}
	}
	cout << -1 << endl;
	return 0;
}

问亿下我怎么错了