#include<bits/stdc++.h>
#define int long long
#define pii pair<int,int>
#define mp make_pair
using namespace std;
typedef long long ll;
int n;
int t[1000005],x[1000005];
inline bool judge(int k){
	int t1=1e9,t2=1e9;
	int p1=x[n],p2=x[n];
	bool vis[1000005];
	memset(vis,0,sizeof(vis));
	for(int i=n;i>=1;i--){
		if(vis[i]) continue;
		bool ava1=0,ava2=0;
		if((t1-t[i])*k>=abs(p1-x[i])){
			ava1=1;
		}
		if((t2-t[i])*k>=abs(p2-x[i])){
			ava2=1;
		}
		if(ava1&&ava2){
			int nexp=-1;
			int tnow=t[i],xnow=x[i];
			for(int j=i;j>=1;j--){
				if((tnow-t[j])*k>=abs(xnow-x[j])){
					vis[j]=1;
					tnow=t[j];
					xnow=x[j];
				}else{
					nexp=j;
					break;
				}
			}
			if(nexp==-1){
				return 1;
			}
			if((t1-t[nexp])*k>=abs(p1-x[nexp])){
				p1=x[nexp];
				t1=t[nexp];
				vis[nexp]=1;
				p2=xnow;
				t2=tnow;
				continue;
			}else if((t2-t[nexp])*k>=abs(p2-x[nexp])){
				p2=x[nexp];
				t2=t[nexp];
				vis[nexp]=1;
				p1=xnow;
				t1=tnow;
				continue;
			}else{
				return 0;
			}
		}else if(ava1){
			vis[i]=1;
			p1=x[i];
			t1=t[i];
		}else if(ava2){
			vis[i]=1;
			p2=x[i];
			t2=t[i];
		}else{
			return 0;
		}
	}
	return 1;
}
signed main(){
//	freopen("coin.in","r",stdin);
//	freopen("coin.out","w",stdout);
	ios::sync_with_stdio(0);
	cin.tie(0);
	cout.tie(0);
	cin>>n;
	int cnt=0;
	int l=0,r=0;
	for(int i=1;i<=n;i++){
		cin>>t[i]>>x[i];
		if(i!=1){
			if(t[i]==t[i-1]){
				cnt++;
				if(cnt==3){
					cout<<"-1\n";
					return 0;
				}
			}else{
				r=max(r,1+abs(x[i]-x[i-1])/(t[i]-t[i-1]));
				cnt=1;
			}
		}
	}
	while(l<r){
		int mid=(l+r)>>1;
		if(judge(mid)){
			r=mid;
		}else{
			l=mid+1;
		}
	}
	cout<<l<<'\n';
	return 0;
}