#define _USE_MATH_DEFINES
#include <algorithm>
#include <cstdio>
#include <functional>
#include <iostream>
#include <cfloat>
#include <climits>
#include <cstdlib>
#include <cstring>
#include <cmath>
#include <map>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <time.h>
#include <vector>
#include <random>
#include <cassert>
using namespace std;

#define rep(i, N) for (int i = 0; i < N; i++)
#define pb push_back

typedef long long ll;
typedef unsigned long long ull;
typedef pair<int, int> i_i;
typedef pair<ll, int> ll_i;
typedef pair<int, ll> i_ll;
typedef pair<double, int> d_i;
typedef pair<ll, ll> ll_ll;
typedef pair<double, double> d_d;
typedef vector<int> vi;
struct edge { int v; ll w; };

ll _MOD = 1000000009;
double EPS = 1e-10;
ll INF = LLONG_MAX / 2;

int main() {
	for (;;) {
		int n; cin >> n;
		if (!n) break;
		vector<int> a(n), b(n);
		rep(u, n) scanf("%d%d", &a[u], &b[u]);
		if (n == 2) {
			cout << abs(a[0] - a[1]) << endl;
			continue;
		}
		vector<i_i> ab;
		vector<int> c;
		rep(u, n)
			if (b[u] == 1) c.pb(a[u]);
			else ab.pb(i_i(a[u], b[u] - 2));
		int N = ab.size(), M = c.size();
		if (!N) {
			cout << -1 << endl;
			continue;
		}
		sort(ab.begin(), ab.end());
		ab.front().second++;
		ab.back().second++;
		sort(c.begin(), c.end());
		vector<ll> dp(M + 1, INF);
		dp[0] = 0;
		rep(i, N) {
			int a = ab[i].first, b = ab[i].second;
			vector<ll> _dp(M + 1, INF);
			deque<i_ll> d;
			ll sum = 0;
			rep(j, M + 1) {
				if (!d.empty() && j - d.front().first > b) d.pop_front();
				while (!d.empty() && d.back().second >= dp[j] - sum) d.pop_back();
				d.push_back(i_ll(j, dp[j] - sum));
				if (!d.empty()) _dp[j] = d.front().second + sum;
				if (j < M) sum += abs(c[j] - a);
			}
			dp = _dp;
		}
		ll ans = dp[M] + ab.back().first - ab.front().first;
		if (ans >= INF) ans = -1;
		cout << ans << endl;
	}
}