#include<bits/stdc++.h>
using namespace std;
int n;
int dp[150005],maxright;
struct line{
	int left,right;
}a[150005];
vector<int> ve[150005];
int main(){
	cin>>n;
	for(int i=1;i<=n;i++){
		cin>>a[i].left>>a[i].right;
		a[i].left++,a[i].right++;
		maxright=max(maxright,a[i].right);
		ve[a[i].right].push_back(a[i].left);
	}
	for(int i=1;i<=maxright;i++){
		dp[i]=dp[i-1];
		for(int j=0;j<ve[i].size();j++){
			dp[i]=max(dp[i-1],dp[ve[i][j]-1]+(i-ve[i][j]+1));
		}
		//cout<<dp[i]<<" ";
	}
	cout<<dp[maxright];
	return 0;
}

RT,样例过了，#3 RE,其他WA