18877.cpp

#include <bits/stdc++.h>
#define fastio ios_base::sync_with_stdio(0), cin.tie(0), cout.tie(0)

#define ll long long
using namespace std;

const ll INF = 1e9 + 7;
const ll DIV = 987654321;

int n, m;
pair<ll, ll> arr[101010];

bool ok(ll x)
{   
    ll cur = 0, cnt = 0;
    for(int i =0 ;i < m;i++){
        cur = max(cur , arr[i].first);
        while(cur <= arr[i].second){
            cnt++;
            if(cnt >= n) return 1;
            cur += x;
        }
    }
    return 0;
}

int main()
{
    fastio;
    cin >> n >> m;
    for (int i = 0; i < m; i++)
    {
        cin >> arr[i].first >> arr[i].second;
    }
    sort(arr, arr + m);
    ll ans = 0;
    ll s = 1, e = 1e18;
    while (s <= e)
    {
        ll m = s + e >> 1;
        if(ok(m)) {
            s = m + 1;
            ans = m;
        }
        else e = m - 1;
    }
    cout << ans << "\n";
    return 0;
}