#include <fstream>

using namespace std;
ifstream fin("buline.in");
ofstream fout("buline.out");
long long n,i,d,s,st,b,j;
int a[400001];
int main()
{
    fin>>n;
    for(i=1;i<=n;i++)
    {
        fin>>a[i]>>b;
        if(b==0) a[i]=0-a[i];
        a[n+i]=a[i];
    }
    for(i=1;i<=n;i++)
    {
        d=d+a[i];
        if(d>st) st=d;
        s=d;
        for(j=i+1;j<=n;j++)
        {
            s=s-a[j-i]+a[j];
            if(s>st) st=s;
        }
    }
    fout<<st;
    return 0;
}