cf 706A

#include<stdio.h>
#include<math.h>

int main()
{
    int a, b;
    scanf("%d %d", &a, &b);

    int n, i;
    scanf("%d", &n);

    int x[n], y[n], v[n];
    for(i = 0; i < n; i++) scanf("%d %d %d", &x[i], &y[i], &v[i]);

    double t, min = 999999999;
    for(i = 0; i < n; i++)
    {
        t = sqrt(((x[i] - a) * (x[i] - a)) + ((y[i] - b) * (y[i] - b))) / v[i];
        if(min > t) min = t;
    }
    printf("%0.20lf\n", min);
}