#include<stdio.h>
#define max(a,b) ((a>=b)?a:b)
#define N 100001
int n,m,i,j,k,p,b[N],tmax;
struct in{
int a,b;
} a[N],x;

void heap(int i){
int s,d,max;
while((i<<1)<=m){
 s=i<<1;d=s+1;max=i;
  if(a[max].b<a[s].b||a[max].b==a[s].b&&a[max].a<a[s].a)
   max=s;
  if(d<=m&&a[max].b<a[d].b||a[max].b==a[d].b&&a[max].a<a[d].a)
   max=d;
  if(max-i){
   x=a[i];
   a[i]=a[max];
   a[max]=x;
   i=max;
  }
  else
   return;
}
}

int main(){
FILE *in=fopen("heavymetal.in","r"),*out=fopen("heavymetal.out","w");
fscanf(in,"%d",&n);
for(i=1;i-n-1;i++)
 fscanf(in,"%d%d",&a[i].a,&a[i].b);
m=n;
for(i=n>>1;i;i--)
 heap(i);
for(;m-1;){
 x=a[1];
 a[1]=a[m];
 a[m]=x;
 m--;
 heap(1);
}
j=1;
for(i=1;i-a[n].b-1;i++){
 b[i]=b[i-1];
  for(;a[j].b==i;j++)
   b[i]=max(b[i],b[a[j].a]+a[j].b-a[j].a);
}
fprintf(out,"%d\n",b[a[n].b]);
return 0;
}