#include <fstream>
#include <vector>
using namespace std;
vector <int> v[1<<17];
int n,tM;
int l[1<<17];
int func(int a,int b)
{if(a>b)
 return a;
 else
 return b;}
int main()
{ifstream q("heavymetal.in");
ofstream w("heavymetal.out");
q>>n;
int i,x,y;
for(i=1;i<=n;i++)
  {q>>x>>y;
  v[y].push_back(x);
  tM=func(tM, y);}
int j;
for(i=1;i<=tM;i++)
  {l[i]=l[i-1];
  for(j=0;j<v[i].size();j++)
    l[i]=func(l[i],l[v[i][j]]+i-v[i][j]);}
w<<l[tM]<<"\n";
return 0;
}