#include <fstream.h>
long n,t[1001],i[1001],d[1001],j;
long max(long a ,long b)
{
  if (a>b)
	return a;
  return b;
}
int min(long a ,long b)
{
  if (a<b)
	return a;
  return b;
}
int main()
{
   ifstream f("pachete.in");
   ofstream g("pachete.out");
   f>>n;
   for (j=1;j<=n;j++)
	 f>>i[j]>>d[j];
   t[n+1]=0;
   for (j=n;j>=1;j--)
		t[j]=d[j]+max(0,t[j+1]-i[j]);
   g<<t[1]<<'\n';
   f.close();
   g.close();
   return 0;
}