```go
package main

import (
	"fmt"
	"math"
)

func main() {
	var a, b float64
	fmt.Scan(&a, &b)

	var n int
	fmt.Scan(&n)

	minTime := math.MaxFloat64

	for i := 0; i < n; i++ {
		var x, y, v float64
		fmt.Scan(&x, &y, &v)

		dist := math.Hypot(x-a, y-b)
		time := dist / v

		if time < minTime {
			minTime = time
		}
	}

	fmt.Println(minTime)
}
```