char rbuf[2000000];
main(){
	int x,y,c;
	long a=0,b=0;
	char*r;
	read(0,r=rbuf,sizeof rbuf);
	while(*r++-48>=0);
	while(*r){
		x=0;
		while(c=*r++-48,c>=0){
			x=x*10+c;
		}
		y=0;
		while(c=*r++-48,c>=0){
			y=y*10+c;
		}
		a+=x-y;
		if(b<a) b=a;
	}
	printf("%ld",b*2-a);
}