#include <cstdio>
#include <complex>
#include <algorithm>
#include <vector>
#include <map>
using namespace std;

#define N 3002
#define eps 1e-8
#define inf 1e15

typedef complex<double> P;
namespace std {
  int operator<(const P& a, const P& b) {
    if (fabs(real(a)-real(b))>eps) return real(a)<real(b);
    if (fabs(imag(a)-imag(b))>eps) return imag(a)<imag(b);
    return 0;
  }
}

int n;
double sw,sd;
P ps[N];
vector<pair<int,double> > g[N];
map<P,int> intern_tbl;
int done[N];
double tbl[N];

int intern(P p) {
  if (intern_tbl.count(p)) return intern_tbl[p];
  int res=intern_tbl.size();
  intern_tbl[p]=res;
  return res;
}

int calc_x(int a, int b, double& res) {
  double y=imag(ps[a]);
  double x=real(ps[b]);

  double x0=real(ps[b]),x1=real(ps[b+1]);
  double y0=imag(ps[b]),y1=imag(ps[b+1]);
  
  if (fabs(y0-y1)<eps) {
    if (fabs(y0-y)<eps) {
      if (x<x0) {
	res=x0;
      } else if (x1<x) {
	res=x1;
      } else {
	return 0;
      }
    } else {
      return 0;
    }
  } else {
    res=(y-y0)*(x1-x0)/(y1-y0)+x0;
  }
  return x0-eps<res&&res<x1+eps;
}

int main() {
  while(scanf("%d",&n),n) {
    intern_tbl.clear();
    for (int i=0;i<N;++i) {
      g[i].clear();
      tbl[i]=-1;
      done[i]=0;
    }

    scanf("%lf%lf",&sw,&sd);
    for (int i=0;i<n;++i) {
      double x,y; scanf("%lf%lf",&x,&y);
      ps[i]=P(x,y);
    }


    vector<P> nps;
    for (int i=0;i<n;++i) nps.push_back(ps[i]);

    for (int i=0;i<n;++i) {
      double left_x=-inf,right_x=inf;
      for (int j=0;j<n-1;++j) {
	if (j==i-1||j==i) continue;
	
	double x;
	if (calc_x(i,j,x)) {
	  if (x<real(ps[i])&&x>left_x) left_x=x;
	  if (x>real(ps[i])&&x<right_x) right_x=x;
	}
      }

      if (left_x!=-inf&&imag(ps[i-1])-imag(ps[i])>eps) {
	P p(left_x,imag(ps[i]));
	int id0=intern(ps[i]);
	int id1=intern(p);
	double d=abs(ps[i]-p)/sd;
	g[id0].push_back(make_pair(id1,d));
	g[id1].push_back(make_pair(id0,d));
	nps.push_back(p);
      }
      if (right_x!=inf&&imag(ps[i+1])-imag(ps[i])>eps) {
	P p(right_x,imag(ps[i]));
	int id0=intern(ps[i]);
	int id1=intern(p);
	double d=abs(ps[i]-p)/sd;
	g[id0].push_back(make_pair(id1,d));
	g[id1].push_back(make_pair(id0,d));
	nps.push_back(p);
      }
    }

    sort(nps.begin(),nps.end());
    for (int i=0;i<(int)nps.size()-1;++i) {
      int id0=intern(nps[i]);
      int id1=intern(nps[i+1]);
      double d=abs(nps[i+1]-nps[i])/sw;
      g[id0].push_back(make_pair(id1,d));
      g[id1].push_back(make_pair(id0,d));
    }

    int start=intern(ps[0]),goal=intern(ps[n-1]);

    multimap<double,int> mm;
    mm.insert(make_pair(0,start));
    tbl[start]=0;
    while(!mm.empty()) {
      double cost=mm.begin()->first;
      int pos=mm.begin()->second;
      mm.erase(mm.begin());
      if (done[pos]) continue;
      done[pos]=1;
      if (pos==goal) break;
      
      for (int i=0;i<g[pos].size();++i) {
	double ncost=cost+g[pos][i].second;
	int npos=g[pos][i].first;
	if (done[npos]) continue;
	if (tbl[npos]<-0.5||tbl[npos]>ncost) {
	  tbl[npos]=ncost;
	  mm.insert(make_pair(ncost,npos));
	}
      }
    }
    printf("%.6lf\n",tbl[goal]);
  }
}