C :

#include<stdio.h>

#define MAXN 1110100UL
#define INF 0x7fffffff 
#define max(a,b) a>b?a:b
#define min(a,b) a<b?a:b

long long int ave,ans,ANS;
long long int sum,n,l=INF ;
long long int r,mid,v[MAXN],now[MAXN],w[MAXN];

int check(int mid){
	for(int i=1;i<n;++i){
		if(w[i]<mid)
			w[i+1]=w[i+1]+w[i]-mid+v[i]-v[i+1];
		if(w[i]>mid&&w[i]-mid-v[i+1]+v[i]>0)
		    w[i+1]=w[i+1]+w[i]-mid-v[i+1]+v[i];
	}
	if(w[n]>=mid)
		return 1;
	return 0;
}

int main(){
#ifndef MAXN
	freopen("fish.in","r",stdin);
	freopen("fish.out","w",stdout);
#endif	
	scanf("%d",&n);
	for(int i=1;i<=n;++i){
		scanf("%d%d",&v[i],&w[i]);
		now[i]=w[i],sum+=w[i];
		l=min(l,w[i]);
	}r=sum+1;
	while(l<=r){
		mid=(l+r)>>1;
		for(int i=1;i<=n;++i)
		    w[i]=now[i];
		if(check(mid))
			ans=mid,l=mid+1;
		else
		    r=mid-1;
	}printf("%d",ans);
	return 0;
}

C++ :

#include<iostream>
#include<cstdio>
#include<cstring>
#define Maxn 100010
#define int64 long long
using namespace std;
int64 N,a[Maxn]={0},b[Maxn]={0},c[Maxn]={0}; 
void init(){
	cin>>N;
	for(int i=1;i<=N;i++){
		scanf("%d%d",&a[i],&b[i]);
	}
	a[N+1]=a[N];
}
bool ok(int64 mid){
	int64 now=0;
	for(int i=1;i<=N+1;i++) c[i]=b[i];
	for(int i=1;i<=N;i++){
		if(i>1) now-=a[i]-a[i-1];
		if(now<0) now=0;		
		now+=c[i];
		if(now<mid){
			if(i<N){
				c[i+1]-=mid-now+a[i+1]-a[i];
				now=mid;
			}
			else return false;
		}
		now-=mid;
	}
	return true;
}
void work(){
	int64 l=1,r=1000000000;
	while(l<=r){
		int64 mid=(l+r)>>1;
		if(ok(mid)) l=mid+1;
		else r=mid-1;
	}
	cout<<r<<endl;
}
int main(){
	init();
	work();
	return 0;
}