#include <bits/stdc++.h>
using namespace std;
const int maxn = 2e4 + 10;
int f[maxn][2], l[maxn], r[maxn];
int main() {
	int n;
	cin >> n;
	for (int i = 1; i <= n; i++) {
		cin >> l[i] >> r[i];
	}
	f[1][0] = 2 * r[1] - l[1] - 1;
	f[1][1] = r[1] - 1;
	for (int i = 2; i <= n; i++) {
		f[i][1] = min(f[i - 1][1] + abs(l[i] - r[i - 1]) + r[i] - l[i] + 1,
		              f[i - 1][0] + abs(l[i] - l[i - 1]) + r[i] - l[i] + 1);
		f[i][0] = min(f[i - 1][1] + abs(r[i] - r[i - 1]) + r[i] - l[i] + 1,
		              f[i - 1][0] + abs(r[i] - l[i - 1]) + r[i] - l[i] + 1);
	}
	cout << min(f[n][1] + n - r[n], f[n][0] + n - l[n]);
	return 0;
}