30pts求条

//998244353
#include<bits/stdc++.h>
#define itn int
#define int long long
using namespace std;
const int N=1e5+10;
int n,m,maxnum=0,sum,output,head,ls;
struct node
{
	int a,b;
}data[N];

inline int cmp(node x,node y)
{
	if(a.a<b.a)
	{
		return 1;
	}
	return 0;
}

inline int check(int mid)
{
	sum=0;
	head=data[1].a;
	for(int i=1;i<=n;i++)
	{
		if(head<data[i].a)
		{
			head=data[i].a;
		}
		if(head<=data[i].b)
		{
			ls=(data[i].b-head)/mid+1;//ls记录这个区间内能放多少奶牛 
			sum+=ls;
			head=data[i].a+ls*mid;
		}
	}
	if(sum<m)
	{
		return 0;
	}
	else
	{
		return 1;
	}
}

signed main()
{
	scanf("%lld%lld",&m,&n);
	for(int i=1;i<=n;i++)
	{
		scanf("%lld%lld",&data[i].a,&data[i].b);
		maxnum=maxnum>data[i].b?maxnum:data[i].b;
	}
	sort(data+1,data+n+1,cmp);
	int l=0,r=maxnum+1;
	while(l+1<r)
	{
		int mid=(l+r)/2;
		if(check(mid))
		{
			output=max(output,mid);
			l=mid;
		}
		else
		{
			r=mid;
		}
	}
	cout<<output;
}