#include <vector>
#include <utility>
#include <cassert>
#include <algorithm>

namespace nachia{

template<class Elem>
class CsrArray{
public:
    struct ListRange{
        using iterator = typename std::vector<Elem>::iterator;
        iterator begi, endi;
        iterator begin() const { return begi; }
        iterator end() const { return endi; }
        int size() const { return (int)std::distance(begi, endi); }
        Elem& operator[](int i) const { return begi[i]; }
    };
    struct ConstListRange{
        using iterator = typename std::vector<Elem>::const_iterator;
        iterator begi, endi;
        iterator begin() const { return begi; }
        iterator end() const { return endi; }
        int size() const { return (int)std::distance(begi, endi); }
        const Elem& operator[](int i) const { return begi[i]; }
    };
private:
    int m_n;
    std::vector<Elem> m_list;
    std::vector<int> m_pos;
public:
    CsrArray() : m_n(0), m_list(), m_pos() {}
    static CsrArray Construct(int n, std::vector<std::pair<int, Elem>> items){
        CsrArray res;
        res.m_n = n;
        std::vector<int> buf(n+1, 0);
        for(auto& [u,v] : items){ ++buf[u]; }
        for(int i=1; i<=n; i++) buf[i] += buf[i-1];
        res.m_list.resize(buf[n]);
        for(int i=(int)items.size()-1; i>=0; i--){
            res.m_list[--buf[items[i].first]] = std::move(items[i].second);
        }
        res.m_pos = std::move(buf);
        return res;
    }
    static CsrArray FromRaw(std::vector<Elem> list, std::vector<int> pos){
        CsrArray res;
        res.m_n = pos.size() - 1;
        res.m_list = std::move(list);
        res.m_pos = std::move(pos);
        return res;
    }
    ListRange operator[](int u) { return ListRange{ m_list.begin() + m_pos[u], m_list.begin() + m_pos[u+1] }; }
    ConstListRange operator[](int u) const { return ConstListRange{ m_list.begin() + m_pos[u], m_list.begin() + m_pos[u+1] }; }
    int size() const { return m_n; }
    int fullSize() const { return (int)m_list.size(); }
};

} // namespace nachia

namespace nachia{


struct Graph {
public:
    struct Edge{
        int from, to;
        void reverse(){ std::swap(from, to); }
        int xorval() const { return from ^ to; }
    };
    Graph() : m_n(0), m_e(0), m_isUndir(false) {}
    explicit Graph(int n, bool undirected = false, int m = 0) : m_n(n), m_e(m), m_isUndir(undirected) {}
    explicit Graph(int n, const std::vector<std::pair<int, int>>& edges, int undirected = false) : m_n(n), m_isUndir(undirected){
        m_e.resize(edges.size());
        for(std::size_t i=0; i<edges.size(); i++) m_e[i] = { edges[i].first, edges[i].second };
    }
    template<class Cin>
    static Graph Input(Cin& cin, int n, bool undirected, int m, int offset = 0){
        Graph res(n, undirected, m);
        for(int i=0; i<m; i++){
            int u, v; cin >> u >> v;
            res[i].from = u - offset;
            res[i].to = v - offset;
        }
        return res;
    }
    template<class Weight, class Cin>
    static std::pair<Graph, std::vector<Weight>> InputWeighted(Cin& cin, int n, bool undirected, int m, int offset = 0){
        Graph res(n, undirected, m);
        std::vector<Weight> wt(m);
        for(int i=0; i<m; i++){
            int u, v; cin >> u >> v >> wt[i];
            res[i].from = u - offset;
            res[i].to = v - offset;
        }
        return std::make_pair(std::move(res), std::move(wt));
    }
    int numVertices() const noexcept { return m_n; }
    int numEdges() const noexcept { return int(m_e.size()); }
    int addNode() noexcept { return m_n++; }
    int addEdge(int from, int to){ m_e.push_back({ from, to }); return numEdges() - 1; }
    Edge& operator[](int ei) noexcept { return m_e[ei]; }
    const Edge& operator[](int ei) const noexcept { return m_e[ei]; }
    auto begin(){ return m_e.begin(); }
    auto end(){ return m_e.end(); }
    auto begin() const { return m_e.begin(); }
    auto end() const { return m_e.end(); }
    bool isUndirected() const noexcept { return m_isUndir; }
    void reverseEdges() noexcept { for(auto& e : m_e) e.reverse(); }
    void contract(int newV, const std::vector<int>& mapping){
        assert(numVertices() == int(mapping.size()));
        for(int i=0; i<numVertices(); i++) assert(0 <= mapping[i] && mapping[i] < newV);
        for(auto& e : m_e){ e.from = mapping[e.from]; e.to = mapping[e.to]; }
        m_n = newV;
    }
    std::vector<Graph> induce(int num, const std::vector<int>& mapping) const {
        int n = numVertices();
        assert(n == int(mapping.size()));
        for(int i=0; i<n; i++) assert(-1 <= mapping[i] && mapping[i] < num);
        std::vector<int> indexV(n), newV(num);
        for(int i=0; i<n; i++) if(mapping[i] >= 0) indexV[i] = newV[mapping[i]]++;
        std::vector<Graph> res; res.reserve(num);
        for(int i=0; i<num; i++) res.emplace_back(newV[i], isUndirected());
        for(auto e : m_e) if(mapping[e.from] == mapping[e.to] && mapping[e.to] >= 0) res[mapping[e.to]].addEdge(indexV[e.from], indexV[e.to]);
        return res;
    }
    CsrArray<int> getEdgeIndexArray(bool undirected) const {
        std::vector<std::pair<int, int>> src;
        src.reserve(numEdges() * (undirected ? 2 : 1));
        for(int i=0; i<numEdges(); i++){
            auto e = operator[](i);
            src.emplace_back(e.from, i);
            if(undirected) src.emplace_back(e.to, i);
        }
        return CsrArray<int>::Construct(numVertices(), src);
    }
    CsrArray<int> getEdgeIndexArray() const { return getEdgeIndexArray(isUndirected()); }
    CsrArray<int> getAdjacencyArray(bool undirected) const {
        std::vector<std::pair<int, int>> src;
        src.reserve(numEdges() * (undirected ? 2 : 1));
        for(auto e : m_e){
            src.emplace_back(e.from, e.to);
            if(undirected) src.emplace_back(e.to, e.from);
        }
        return CsrArray<int>::Construct(numVertices(), src);
    }
    CsrArray<int> getAdjacencyArray() const { return getAdjacencyArray(isUndirected()); }
private:
    int m_n;
    std::vector<Edge> m_e;
    bool m_isUndir;
};

} // namespace nachia

#include <iostream>
#include <queue>
using namespace std;
using ll = long long;
using ull = unsigned long long;
#define rep(i,n) for(int i=0; i<(n); i++)

template<class T>
using nega_queue = priority_queue<T,vector<T>,greater<T>>;

const int INF = 1001001001;

const int W = 600;
const int H = 600;
const int NV = W * H; // number of vertices
const int maxV = 7;

struct Start{ int id,v; };

int pos2id(int y,int x){ return y * W + x; }

int X,Y;
int N;
vector<Start> hikyaku;
double dt[maxV];
double V[maxV];
double T[maxV][NV];

double D[maxV][NV];

int main(){
  cin >> X >> Y; X--; Y--;
  cin >> N;

  auto graph = nachia::Graph(H*W, true);
  rep(y,H) rep(x,W-1) graph.addEdge(pos2id(y,x), pos2id(y,x+1));
  rep(y,H-1) rep(x,W) graph.addEdge(pos2id(y,x), pos2id(y+1,x));
  auto E = graph.getAdjacencyArray();

  hikyaku.resize(N);
  rep(i,N){
    int x,y,v; cin >> x >> y >> v;
    x--; y--; v--;
    hikyaku[i] = { pos2id(y,x),v };
  }

  rep(v,maxV) V[v] = 1+v;
  rep(v,maxV) dt[v] = 1.0 / (1+v);
  
  rep(v,maxV) rep(i,NV) T[v][i] = 1.0e100;

  {
    vector<vector<int>> I(maxV);
    for(auto a : hikyaku){
      I[a.v].push_back(a.id);
      T[a.v][a.id] = 0;
    }
    rep(v,maxV){
      rep(i,I[v].size()){
        int p = I[v][i];
        for(int e : E[p]) if(T[v][e] >= 1.0e50){
          T[v][e] = T[v][p] + dt[v];
          I[v].push_back(e);
        }
      }
    }
  }
  
  rep(v,maxV) rep(i,NV) D[v][i] = 1.0e100;

  nega_queue<pair<double,pair<int,int>>> Q;
  D[hikyaku[0].v][hikyaku[0].id] = 0.0;
  Q.push(make_pair(0.0,make_pair(hikyaku[0].v,hikyaku[0].id)));

  auto see = [&](double nxd, int nxv, int p) {
    if(D[nxv][p] > nxd){
      D[nxv][p] = nxd;
      Q.push(make_pair(D[nxv][p],make_pair(nxv,p)));
    }
  };

  while(Q.size()){
    double d = Q.top().first;
    int v = Q.top().second.first;
    int p = Q.top().second.second;
    Q.pop();
    if(D[v][p] != d) continue;
    for(int nxv=v+1; nxv<maxV; nxv++) see(max(T[nxv][p],d), nxv, p);
    for(int e : E[p]){
      see(d + dt[v], v, e);
      double nxd = dt[v];
      vector<double> buf(maxV, 1.0e100);
      buf[v] = d + dt[v];
      for(int nxv=v+1; nxv<maxV; nxv++) if(T[nxv][e] < INF/2){
        for(int w=v; w<nxv; w++) if(buf[w] < 1.0e50){
          double pt = (buf[w] - T[nxv][e]) * V[w];
          if(pt > 1.0 || 0.0 > pt) continue;
          buf[nxv] = min(buf[nxv], T[nxv][e] + pt / (V[w] + V[nxv]) * 2);
        }
        if(buf[nxv] < 1.0e50) see(buf[nxv], nxv, e);
      }
    }
  }

  double ans = INF;
  rep(v,maxV) ans = min(ans,D[v][pos2id(Y,X)]);
  cout.precision(10); cout << fixed;
  ans *= 1000.0;
  cout << ans << endl;
  return 0;
}

struct ios_do_not_sync{
  ios_do_not_sync(){
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
  }
} ios_do_not_sync_inst;