#include <bits/stdc++.h>
using namespace std;
int n, a[20005][2], f[20005][2];//0=left,1=right
int main()
{
	cin >> n;
	for(int i = 1; i <= n; i++)cin >> a[i][0] >> a[i][1];
	f[1][0] = a[1][0] + (a[1][1] - a[1][0]) * 2;
	f[1][1] = a[1][1];
	for(int i = 2; i <= n; i++)
	{
		f[i][0] = min(f[i - 1][1] + abs(a[i][0] - a[i - 1][1]), f[i - 1][0] + abs(a[i][1] - a[i - 1][0])) + a[i][1] - a[i][0] + 1;
		f[i][1] = min(f[i - 1][1] + abs(a[i][1] - a[i - 1][1]), f[i - 1][0] + abs(a[i][0] - a[i - 1][0])) + a[i][1] - a[i][0] + 1;
	}
	cout << min(f[n][0], f[n][1]);
	return 0;
}