codeforces #313 div1 E

#include<cstdio>
#include<cstring>
#include<iostream>
#include<algorithm>
#include<cstdlib>
#include<vector>
using namespace std;

typedef long long LL;
const int maxn=310;
const LL oo=1LL<<62;
int n,m,a[maxn],b[maxn],p[maxn],L[maxn],R[maxn];
LL dp[maxn][maxn][maxn],ans;
vector<int>V;
void cmax(LL &a,LL b){if(a<b)a=b;}

int main(){
	scanf("%d",&n);
	for(int i=0;i<n;++i){
		scanf("%d%d",&a[i],&b[i]);
		V.push_back(a[i]);V.push_back(a[i]+b[i]);V.push_back(a[i]-b[i]);
	}
	sort(V.begin(),V.end());
	V.erase(unique(V.begin(),V.end()),V.end());
	for(int i=0;i<n;++i){
		p[i]=lower_bound(V.begin(),V.end(),a[i])-V.begin();
		L[i]=lower_bound(V.begin(),V.end(),a[i]-b[i])-V.begin();
		R[i]=lower_bound(V.begin(),V.end(),a[i]+b[i])-V.begin();
	}
	m=V.size();
	for(int i=0;i<m;++i){
		for(int j=0;j<m;++j){
			for(int k=0;k<m;++k){
				dp[i][j][k]=-oo;
			}
		}
	}
	for(int i=0;i<m;++i)dp[0][0][i]=0;
	for(int i=0;i<m-1;++i){
		int pos=-1;
		for(int j=0;j<n;++j)if(p[j]==i)pos=j;
		for(int j=0;j<m;++j){
			for(int k=0;k<m;++k){
				if(dp[i][j][k]>=0){
					if(pos==-1){
						cmax(dp[i+1][j][k],dp[i][j][k]+(j>=i+1||k<=i?(V[i+1]-V[i]):0));
					}else{
						cmax(dp[i+1][max(j,R[pos])][k],dp[i][j][k]+V[i+1]-V[i]);
						if(k==L[pos]){
							for(int l=k;l<m;++l)cmax(dp[i+1][max(j,i)][l],dp[i][j][k]+(j>=i+1||l<=i?(V[i+1]-V[i]):0));
						}
					}
				}
			}
		}
	}
	ans=0;
	for(int i=0;i<m;++i)cmax(ans,dp[m-1][i][m-1]);
	printf("%I64d\n",ans);
	return 0;
}