#include<iostream>
#include<string>
#include<cstdio>
#include<vector>
#include<cmath>
#include<algorithm>
#include<functional>
#include<iomanip>
#include<queue>
#include<ciso646>
#include<random>
#include<map>
#include<set>
#include<bitset>
#include<stack>
#include<unordered_map>
#include<utility>
#include<cassert>
#include<complex>
#include<numeric>
using namespace std;

//#define int long long
typedef long long ll;

typedef unsigned long long ul;
typedef unsigned int ui;
constexpr ll mod = 998244353/100;
const ll INF = mod * mod;
typedef pair<int, int>P;
#define stop char nyaa;cin>>nyaa;
#define rep(i,n) for(int i=0;i<n;i++)
#define per(i,n) for(int i=n-1;i>=0;i--)
#define Rep(i,sta,n) for(int i=sta;i<n;i++)
#define rep1(i,n) for(int i=1;i<=n;i++)
#define per1(i,n) for(int i=n;i>=1;i--)
#define Rep1(i,sta,n) for(int i=sta;i<=n;i++)
#define all(v) (v).begin(),(v).end()
typedef pair<ll, ll> LP;
typedef double ld;
typedef pair<ld, ld> LDP;
const ld eps = 1e-12;
const ld pi = acos(-1.0);

ll mod_pow(ll x, ll n, ll m) {
	ll res = 1;
	while (n) {
		if (n & 1)res = res * x % m;
		x = x * x % m; n >>= 1;
	}
	return res;
}
struct modint {
	ll n;
	modint() :n(0) { ; }
	modint(ll m) :n(m) {
		if (n >= mod)n %= mod;
		else if (n < 0)n = (n % mod + mod) % mod;
	}
	operator int() { return n; }
};
bool operator==(modint a, modint b) { return a.n == b.n; }
modint operator+=(modint& a, modint b) { a.n += b.n; if (a.n >= mod)a.n -= mod; return a; }
modint operator-=(modint& a, modint b) { a.n -= b.n; if (a.n < 0)a.n += mod; return a; }
modint operator*=(modint& a, modint b) { a.n = ((ll)a.n * b.n) % mod; return a; }
modint operator+(modint a, modint b) { return a += b; }
modint operator-(modint a, modint b) { return a -= b; }
modint operator*(modint a, modint b) { return a *= b; }
modint operator^(modint a, ll n) {
	if (n == 0)return modint(1);
	modint res = (a * a) ^ (n / 2);
	if (n % 2)res = res * a;
	return res;
}

ll inv(ll a, ll p) {
	return (a == 1 ? 1 : (1 - p * inv(p % a, a)) / a + p);
}
modint operator/(modint a, modint b) { return a * modint(inv(b, mod)); }

const int max_n = 1 << 22;
modint fact[max_n], factinv[max_n];
void init_f() {
	fact[0] = modint(1);
	for (int i = 0; i < max_n - 1; i++) {
		fact[i + 1] = fact[i] * modint(i + 1);
	}
	factinv[max_n - 1] = modint(1) / fact[max_n - 1];
	for (int i = max_n - 2; i >= 0; i--) {
		factinv[i] = factinv[i + 1] * modint(i + 1);
	}
}
modint comb(int a, int b) {
	if (a < 0 || b < 0 || a < b)return 0;
	return fact[a] * factinv[b] * factinv[a - b];
}

ll gcd(ll a, ll b) {
	if (a < b)swap(a, b);
	while (b) {
		ll r = a % b; a = b; b = r;
	}
	return a;
}

using speP = pair<int, P>;
int cost[50][50];
int dist[50][50];

int swcost[50][50];
int n, m;
void solve() {
	vector<int> d(n), h(n);
	rep(i, n) {
		if (i == 0) {
			d[i] = 0, h[i] = 0;
		}
		else if (i == n - 1) {
			d[i] = 0, h[i] = 1000;
		}
		else {
			cin >> d[i] >> h[i];
		}
	}
	rep(i, n)rep(j, n) {
		if (i == j)cost[i][j] = 0;
		else cost[i][j] = mod;
	}
	rep(i, m) {
		int a, b, c; cin >> a >> b >> c; a--; b--;
		cost[a][b] = c;
	}
	rep(i, n) {
		rep(j, n) {
			swcost[i][j] = mod;
		}
		swcost[i][i] = d[i];
		priority_queue<P, vector<P>, greater<P>> q;
		q.push({ d[i],i });
		while (!q.empty()) {
			P p = q.top(); q.pop();
			int id = p.second;
			if (swcost[i][id] < p.first)continue;
			rep(to, n) {
				if (h[id] != h[to])continue;
				int nd = p.first + d[to] + 2 * cost[id][to];
				if (nd < swcost[i][to]) {
					swcost[i][to] = nd;
					q.push({ nd,to });
				}
			}
		}
		rep(j, n) {
			swcost[i][j] -= d[i] + d[j];
		}
	}

	rep(i, n)rep(j, n)dist[i][j] = mod;
	dist[0][0] = 0;
	priority_queue<speP, vector<speP>, greater<speP>> q;
	q.push({ 0,{0,0} });
	while (!q.empty()) {
		speP p = q.top(); q.pop();
		int x = p.second.first, y = p.second.second;
		if (dist[x][y] < p.first)continue;
		rep(nx, n) {
			if (h[x] > h[nx])continue;
			int s = p.first + cost[x][nx] + d[nx];
			if (s < dist[nx][y]) {
				dist[nx][y] = s;
				q.push({ s,{nx,y} });
			}
		}
		rep(ny, n) {
			if (h[y] > h[ny])continue;
			int s = p.first + cost[ny][y] + d[ny];
			if (s < dist[x][ny]) {
				dist[x][ny] = s;
				q.push({ s,{x,ny} });
			}
		}
		if (h[x] == h[y]&&x!=y) {
			int s = p.first + swcost[x][y];
			if (s < dist[y][x]) {
				dist[y][x] = s;
				q.push({ s,{y,x} });
			}
		}
		rep(nx, n)rep(ny, n) {
			if (h[x] > h[nx] || h[y] > h[ny])continue;
			int s = p.first + cost[x][nx] + cost[ny][y] + d[nx] + d[ny];
			if (nx == ny)s -= d[nx];
			if (s < dist[nx][ny]) {
				//cout << "? " << x << " " << y << " " << nx << " " << ny << " " << s << "\n";
				dist[nx][ny] = s;
				q.push({ s,{nx,ny} });
			}
		}
	}
	/*rep(i, n) {
		rep(j, n)cout << dist[i][j] << " ";
		cout << "\n";
	}*/
	//cout << dist[1][2]<<" "<<swcost[1][2] << "\n";
	int ans = dist[n - 1][n - 1];
	if (ans == mod)cout << -1 << "\n";
	else cout << ans << "\n";
}




signed main() {
	ios::sync_with_stdio(false);
	cin.tie(0);
	//cout << fixed << setprecision(10);
	//init_f();
	//expr();
	//int t; cin >> t; rep(i, t)
	while (cin >> n >> m, n)
		solve();
	return 0;
}
