#include <iostream>
#include <cstdlib>
#include <stack>
using namespace std;
int d (const void* a,const void* b){unsigned int* p1=(unsigned int*)a;unsigned int* p2=(unsigned int*)b;
return p1[0] - p2[0];}int main(){unsigned int a,b,c,e,f,i,j,k,n;stack<unsigned int> q;
stack<unsigned int> r;cin>>n>>k>>a>>b;k=2*k;unsigned int p[k][2];
unsigned int *g,*h[n+1],l[n+1];int m[n+1],o[n+1];for(i=0;i<k;i+=2){cin>>p[i][0]>>p[i][1];
p[i+1][1]=p[i][0];p[i+1][0]=p[i][1];}qsort(p,k,2*sizeof(unsigned int),d);i=j=0;
while(i<k){h[p[i][0]]=p[i];l[p[i][0]]=1;j++;while(p[i][0]==p[j][0]&&j<k){l[p[i][0]]++;
j++;}i=j;}if(a==b){cout<<a;return 0;}if(a<b){if(h[1]==NULL){cout<<b;return 0;}
m[1]=1;for(i=2;i<=n;i++)m[i]=0;e=a;g=h[1];for(i=0;i<l[1];i++){c=g[1];m[c]=1;
if(c==n){cout<<a;return 0;}r.push(c);g+=2;}while(!r.empty()){swap(q,r);e=e+a;if(e>=b)
{cout<<b;return 0;}while(!q.empty()){f=q.top();q.pop();g=h[f];
for(j=0;j<l[f];j++){c=g[1];if(m[c]==0){if(c==n&&e<b){cout<<e;return 0;}m[c]=1;
r.push(c);}g+=2;}}}cout<<b;return 0;}else{if(h[1]==NULL){cout<<b;return 0;}m[1]=1;
e=b;g=h[1];for(i=2;i<=n;i++){o[i]=0;}for(i=0;i<l[1];i++){c=g[1];o[c]=1;g+=2;}
for(i=2;i<=n;i++){if(o[i]==0){r.push(i);m[i]=1;}else m[i]=0;}while(!r.empty()){
swap(q, r);e=e+b;if(e>=a){cout<<a;return 0;}while(!q.empty()){f=q.top();q.pop();
g=h[f];for(i=2;i<=n;i++){o[i]=0;}for(j=0;j<l[f];j++){c=g[1];o[c]=1;g+=2;}
if(o[n]==0&&e<a){cout<<e;return 0;}for(i=2;i<n;i++){if(o[i]==0&&m[i]==0){m[i]=1;
r.push(i);}}}}cout<<a;return 0;}}