#include<bits/stdc++.h>
using namespace std;
int main(){
int N,ans=0;
cin>>N;
int left[N],right[N];
for(int i = 0;i<N;i++){
cin>>left[i]>>right[i];
}
for(int i = 0;i<N;i++){
if(right[i]==0 && left[i]==0){
continue;
}
for(int j = 0;j<i;j++){
if(right[j]==0 && left[j]==0){
continue;
}
if(min(right[i],right[j])>max(left[i],left[j])&& i!=j){
right[i] = max(right[i],right[j]);
left[i] = min(left[i],left[j]);
right[j] = 0;
left[j] = 0;
}
}
}
for(int i = 0;i<N;i++){
ans+=right[i]-left[i];
}
cout<<ans<<endl;
return 0;
}