#include <bits/stdc++.h>
using namespace std;

typedef long long ll;
ll n, m, p[100005], a[100005], b[100005], c[100005];
ll d[100005], cnt[100005];
int main()
{
    ios::sync_with_stdio(false);
    cin.tie(0);
    cin >> n >> m;
    for (int i = 1; i <= m; i++)
    {
        cin >> a[i];
    }
    for (int i = 1; i < m; i++)
    {
        if (a[i] <= a[i + 1])
        {
            d[a[i]]++;
            d[a[i + 1]]--;
        }
        else
        {
            d[a[i + 1]]++;
            d[a[i]]--;
        }
    }
    for (int i = 1; i <= n - 1; i++)
    {
        cnt[i] = cnt[i - 1] + d[i];
    }
    ll ans = 0;
    for (int i = 1; i <= n - 1; i++)
    {
        cin >> a[i] >> b[i] >> c[i];
        ans += min(a[i] * cnt[i], b[i] * cnt[i] + c[i]);
    }
    cout << ans << endl;
    return 0;
}