#include<stdio.h>
#define dim 10001
int i,k,n;
int a[dim],t[dim];
int vec[dim],timp[dim];
void bubble()
{
    int x=1;
    int aux;
    while(x)
    {
            x=0;
            for(i=1;i<n;i++)
            if(a[i]>a[i+1])
            {
                           aux=a[i];
                           a[i]=a[i+1];
                           a[i+1]=aux;
                           aux=t[i];
                           t[i]=t[i+1];
                           t[i+1]=aux;
                           x=1;
                           }
                           }
}
void read()
{
     scanf("%d",&n);
     for(i=1;i<=n;i++)
     scanf("%d%d",&a[i],&t[i]);
     bubble();
     
}
void solve()
{
     read();
     int p;
    
     int max,vmax;
     for(i=1;i<=n;i++)
     {// printf("%d\n",n);
                      p=max=vmax=0;
                      for(k=1;k<i;k++)
                      {
                                      if(timp[k]>max && vec[k]<=a[i])
                                                 {
                                                         max=timp[k];
                                                         p=k;
                       }                                  }
                       
                      vec[i]=t[i];
                      timp[i]=(t[i]-a[i])+timp[p];
                     /// printf("%d %d \n",timp[i],vec[i]);
                      }
                      max=0;
     for(i=1;i<=n;i++)
    // printf("%d %d \n",timp[i],vec[i]);
    if(max<timp[i])
    max=timp[i];
    printf("%d",max);
    
}
int main ()
{
    freopen("heavymetal.in","r",stdin);
    freopen("heavymetal.out","w",stdout);
    solve();
    return 0;
}