#include<stdio.h>

#define input "pachete.in"
#define output "pachete.out"

int n, inst, down, ti, td;

int main()
{
	FILE *in, *out;

	in = fopen (input, "r");
	out = fopen (output, "w");

	int i;

	fscanf(in, "%d", &n);

	ti = 0;
	td = 0;

	for(i=1; i<=n; i++)
	{
		fscanf(in, "%d%d", &inst, &down);

		if(down >= ti)
		{
			td += down-ti;

			ti = 0;
		}
		else

			ti -= down;

		ti+=inst;

	}

	fprintf(out, "%d", td);

	return 0;

}