#include<cstdio>
#include<algorithm>

using namespace std;

int n, L, S, v[20000], x[20000], l[20000], sum[20000], s;
double t[20000];

int main()
{
    while(1)
    {
        scanf("%d%d%d%d", &n, &L, &S, &v[0]);
        if (n == 0)
            break;
        for (int i = 1; i <= n; i++)
        {
            scanf("%d%d%d", &x[i], &l[i], &v[i]);
            sum[i] = sum[i - 1] + L + l[i];
        }
        for (int i = n; i >= 0; i--)
        {
            s = S + sum[i];
            if (s <= x[i])
            {
                t[i] = 0;
                continue;
            }
            if (i == n)
                t[i] = (double) (s - x[i]) / (double) v[i];
            else
                t[i] = max((double)(s - x[i]) / (double) v[i], t[i + 1]);
        }
        printf("%.20lf\n", t[0]);
    }
    return 0;
}