#include <bits/stdc++.h>
using namespace std;
const int N=1e6+7;
int n,a[N],b[N]; 
map<int,int>mapp;
priority_queue<int>q;
int main(){
    freopen("nit.in","r",stdin);
    freopen("nit.out","w",stdout);    
    cin>>n;
    for(int i=1;i<=n;i++){
        cin>>a[i]>>b[i];
        mapp[a[i]]=b[i];
        q.push(-a[i]);
    }
    int ans=0;
    while(!q.empty()){
        int c=-q.top();
        q.pop();
        int d;
        if(-q.top()>mapp[c]&&!q.empty()){
            d=-q.top();
            q.pop();
            q.push(-mapp[c]);
        }
        else{
            d=mapp[c];
        }
        
        ans+=(c-d);
    }
    cout<<ans;

    return 0; 
}