// yuki 999 てん vs. ほむ
// 2020.2.28 bal4u

#include <stdio.h>

typedef long long ll;

int getchar_unlocked(void);
#define gc() getchar_unlocked()

int in() {  // 整数の入力
	int n = 0; int c = gc();
	do n = 10*n + (c & 0xf), c = gc(); while (c >= '0');
	return n;
}

ll s[100005];
int main()
{
	int i, N;
	ll ans, t;

	N = in();
	for (i = 1; i <= N; ++i) {
		s[i] = s[i-1] + (in() - in());
	}
	ans = -0xfffffffffffffffLL;
	for (i = 0; i <= N; ++i) {
		t = (s[i] << 1);
		if (t > ans) ans = t;
	}
	printf("%lld\n", ans-s[N]);
	return 0;
}