#include<stdio.h>

typedef struct {
        long x, y;
        }Spectacol;

Spectacol *v, aux;
long n, i, *L, *poz;
long max, pozj, j, s=0;

void citire(){
     freopen("heavymetal.in","r",stdin);
     scanf("%ld",&n);
     v=new Spectacol[n+1];
     L=new long[n+1];
     poz=new long[n+1];
     for(i=1; i<=n; i++) scanf("%ld %ld\n", &v[i].x, &v[i].y);
     fclose(stdin);
}

void qsort(int x, int y){
     int i=x, j=y, mx, my;
     mx=v[(x+y)/2].x;
     my=v[(x+y)/2].y;
     while(i<=j){
		 while( (v[i].y<my) || (v[i].y==my && v[i].x<mx) ) i++;
		 while( (v[j].y>my) || (v[j].y==my && v[j].x>mx) ) j--;
                 if(i<=j){
                          aux=v[i];
                          v[i]=v[j];
                          v[j]=aux;
			  i++;
                          j--;
			  }
                 }
     if(x<j) qsort(x,j);
     if(i<y) qsort(i,y);
}

void apd(){
     L[1]=v[1].y-v[1].x;

     poz[1]=0;
     for(i=2; i<=n; i++){
              L[i]=v[i].y-v[i].x;
              max=0;
              for(j=1; j<i; j++){
                       if(L[j]>max && v[j].y<=v[i].x){
                                   max=L[j];
                                   pozj=j;
                                   }
                       }
	      L[i]+=L[pozj];
              poz[i]=pozj;
              }
     }

void solutie(){
     //s=0;
     //for(i=n; i>=1; i=poz[i]) s+=L[i];
     freopen("heavymetal.out","w",stdout);
     printf("%ld\n",L[n]);
     fclose(stdout);
     }

int main(){
    citire();
    qsort(1,n);
    apd();
    solutie();
    return 0;
}