#include<fstream>
#include<algorithm>
using namespace std;
int i, n, p, u, mij, sol, a[100003];
struct cub{
    int p;
    int u;
};
int cmp(cub x, cub y){
    if(x.u!=y.u)
        return x.u<y.u;
    else
        return x.p<y.p;
}
cub v[100003];
FILE*fin=fopen("heavymetal.in","r");
ofstream fout("heavymetal.out");
int main(){
    fscanf(fin,"%d", &n);
    for(i=1; i<=n; i++){
        fscanf(fin,"%d%d",&v[i].p, &v[i].u);
    }
    sort(v+1, v+n+1, cmp);
    a[1]=v[1].u-v[1].p;
    for(i=2; i<=n; i++){
        p=1; u=i-1;
        sol=0;a[i]=a[i-1];
        while(p<=u){
            mij=p+(u-p)/2;
            if(v[i].p>=v[mij].u){
            //if(v[i].u>=v[mij].p){
                sol=mij;
                p=mij+1;
            }
            else
                u=mij-1;
        }
     if(a[i]<a[sol]+v[i].u-v[i].p)
         a[i]=a[sol]+v[i].u-v[i].p;
    }
    fout<<a[n];
    return 0;
}