#include <stdio.h>

int n,i,j,Best[100000],b[100000],a[100000],maxim;
int max(int a,int b)
{
    if (a>b)
    return a;
    else
    return b;
}

int main()
{
    freopen("heavymetal.in","rt",stdin);
    scanf("%d", &n);
    for (i=1;i<=n;++i)
          {
           scanf("%d %d", &a[i], &b[i]);
           maxim=max(maxim,b[i]);
        }
        
    for (i=1;i<=maxim;++i)
          {    
           Best[i]=Best[i-1];   
           for (j=1;j<=maxim;++j)
           if (b[j]==i)   
        Best[i] = max(Best[i],Best[a[j]]+(b[j]-a[j]));  
}

freopen("heavymetal.out","wt",stdout);
printf("%d", Best[maxim]);
return 0;
}