#include<stdio.h>
int v[100],a,s,sum,m[101],i,n;
int main(){
	FILE*f=fopen("buline.in","r");
	FILE*g=fopen("buline.out","w");
	fscanf(f,"%d ",&n);
	for(i=1;i<=n;i++){
		fscanf(f,"%d %d",&a,&s);
		if(s>0)
			v[i]=a;
		else
			v[i]-=a;
		}
	for(i=1;i<=n;i++)
		sum+=v[i];
	m[1]=v[1];
	for(i=2;i<=n;i++)
		if(v[i]<(m[i-1]+m[i]))
			m[i+1]=m[i-1]+m[i];

	fclose(f);
	fclose(g);
	return 0;

}