感觉思路是对的但为啥不行？（样例过）

#include<bits/stdc++.h>
using namespace std;
#define ll long long
const int N=2e5+5;
int n,m;
struct node
{
	ll x,t;
}w[N];
ll maxx=-INT_MAX;
ll js(node a,node b)
{
	return llabs((a.x-b.x))/llabs((a.t-b.t));
}
int main()
{
	cin>>n>>m;
	for(int i=1;i<=n;i++)
		cin>>w[i].x>>w[i].t;
	for(int i=1;i<=n-1;i++)
	{
		maxx=max(maxx,js(w[i],w[i+1]));
		/*cout<<"ss"<<maxx<<endl;*/
	}
	for(int z=1;z<=m;z++)
	{
		int a,b;
		ll last,lasttime,maxxx=maxx;
		cin>>a>>b;
		lasttime=w[a].t; w[a].t=b;
		last=max(js(w[a],w[a-1]),js(w[a],w[a+1]));
		maxx=max(maxx,last);
		cout<<maxx<<endl;
		maxx=maxxx;w[a].t=c;
	}
	return 0;
}