#include <algorithm>
#include <fstream>

using namespace std;

const long pinf = 1<<30;
ifstream f("input");
ofstream g("output");

long heap[500005],poz[500005],d[500005];
long n,m,i,a,b;

struct nod
{
    long cost,val;
    nod *next;
}*p,*l[500001];

void citire(long &n,long &k,long &a,long &b)
{
    long x,y,i,j;
    nod *p;

    f>>n>>k>>a>>b;

    for(i=1;i<n;i++)
        for(j=i+1;j<=n;j++)
    {
        p=new nod;
        p->val=j;
        p->cost=b;
        p->next=l[i];
        l[i]=p;
        p=new nod;
        p->val=i;
        p->cost=b;
        p->next=l[j];
        l[j]=p;
    }
    for(i=1;i<=k;i++)
    {
        f>>x>>y;
        for(p=l[x];p->val!=y;p=p->next);
        p->cost=a;
        for(p=l[y];p->val!=x;p=p->next);
        p->cost=a;
    }

}

void urca(long pozi)
{
    while(pozi>1&& d[heap[pozi]]<=d[heap[pozi/2]])
    {
        swap(heap[pozi],heap[pozi/2]);
        poz[heap[pozi]]=pozi;
        poz[heap[pozi/2]]=pozi/2;
        pozi/=2;

    }
}

void coboara(long pozi)
{
 {
    long poz1=0;

    while(pozi!=poz1) {
        poz1=pozi;

        if(2*poz1<=n && d[heap[pozi]]>d[heap[2*poz1]])
            pozi=2*poz1;
        if(2*poz1+1<=n && d[heap[pozi]]>d[heap[2*poz1+1]])
            pozi=2*poz1+1;

        swap(heap[pozi],heap[poz1]);
        poz[heap[pozi]]=pozi;
        poz[heap[poz1]]=poz1;

        }
}}


int main()
{
    citire(n,m,a,b);
    long ni=n,x;

    for(i=1;i<=n;i++)
    {
        d[i]=pinf;
        heap[i]=poz[i]=i;
    }
    d[1]=0;
    for(i=1;i<=ni;i++)
    {
        x=heap[1];
        swap (heap[1],heap[n]);
        swap (poz[heap[1]],poz[heap[n]]);
        n--;
        coboara(1);
        for(p=l[x];p!=NULL;p=p->next)
                if(d[p->val]>d[x]+p->cost)
            {
            d[p->val]=d[x]+p->cost;
            urca(poz[p->val]);
            }
        }

    g<<d[ni];
    return 0;
}