#include <cstdio>#include <iostream>#include <algorithm>#define max(x, y) ((x) > (y) ? (x) : (y))int n, v;int f[3000001];struct node{	int x, y;}p[150001];inline int read(){	int x = 0, f = 1;	char ch = getchar();	for(; !isdigit(ch); ch = getchar()) if(ch == ‘-‘) f = -1;	for(; isdigit(ch); ch = getchar()) x = (x << 1) + (x << 3) + ch - ‘0‘;	return x * f;}inline bool cmp(node a, node b){	return a.x < b.x;}int main(){	int i, j = 1;	n = read();	for(i = 1; i <= n; i++) p[i].x = read(), p[i].y = read(), v = max(v, p[i].y);	std::sort(p + 1, p + n + 1, cmp);	for(; !p[j].x; j++) f[p[j].y] = p[j].y + 1;	for(i = 1; i <= v; i++)	{		f[i] = max(f[i], f[i - 1]);		for(; p[j].x == i; j++) f[p[j].y] = max(f[p[j].y], f[i - 1] + p[j].y - p[j].x + 1);	}	printf("%d\n", f[v]);	return 0;}