#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;
}

问一下我怎么错了呢？