简单题。
#pragma comment(linker, "/STACK:1024000000,1024000000")
#include<cstdio>
#include<cstring>
#include<cmath>
#include<algorithm>
#include<vector>
#include<map>
#include<set>
#include<queue>
#include<stack>
#include<iostream>
using namespace std;
typedef long long LL;
const double pi=acos(-1.0),eps=1e-;
void File()
{
freopen("D:\\in.txt","r",stdin);
freopen("D:\\out.txt","w",stdout);
} int x,y,n; int main()
{
scanf("%d%d",&x,&y);
scanf("%d",&n);
double ans=;
for(int i=;i<=n;i++)
{
int tx,ty,v;
scanf("%d%d%d",&tx,&ty,&v);
double t=sqrt((tx-x)*(tx-x)+(ty-y)*(ty-y))/v;
ans=min(ans,t);
}
printf("%.6lf\n",ans);
return ;
}