#include <bits/stdc++.h>

using namespace std;

typedef long long ll;

const long long mod = 1e9+;

const int maxn = 5e5+;

const int inf = 1e9+;

int n,m,a,b,nm,qwq;

int head[maxn];

ll dis[maxn];

struct node{

    int to,nxt;

}edg[maxn*];

void add(int x,int y){

    edg[++nm].to = y;

    edg[nm].nxt = head[x];

    head[x]=nm;

    if(x==&&y==n)qwq=;

}

queue<int> p,q;

int f[maxn],dep[maxn];

void solve(){

    dis[]=;

    int i,j,x,y;

    p.push();

    for(i=;i<=n;i++){

        q.push(i);

    }

    for(i=;i<=n;i++){

        f[i]=;dep[i]=;

    }

    while(!p.empty()){

        if(q.empty())break;

        x = p.front();

        p.pop();

        for(i=head[x];i;i=edg[i].nxt)f[edg[i].to]=x;

        j = dep[q.front()];

        while(!q.empty()){

            y = q.front();

            if(dep[y]!=j)break;

            q.pop();

            dep[y]=dep[y]+;

            if(f[y]==x)q.push(y);

            else{

                p.push(y);

                dis[y]=dis[x]+b;

            }

        }

    }

    while(!p.empty())p.pop();

    while(!q.empty())q.pop();

    if(dis[n]==-||dis[n]>a)printf("%d\n",a);

    else printf("%lld\n",dis[n]);

}

void dist(){

    int i,j,x,y;

    dis[]=;

    p.push();

    while(!p.empty()){

        x = p.front();

        p.pop();

        for(i=head[x];i;i=edg[i].nxt){

            y = edg[i].to;

            if(dis[y]!=-)continue;

            dis[y]=dis[x]+a;

            p.push(y);

        }

    }

    if(dis[n]==-||dis[n]>b)printf("%d\n",b);

    else printf("%lld\n",dis[n]);

}

int main()

{

    while(scanf("%d%d%d%d",&n,&m,&a,&b)==){

        qwq=;

        nm = ;

        int i,j,x,y;

        for(i=;i<=n;i++){

            head[i]=;

            dis[i]=-;

        }

        for(i=;i<=m;i++){

            scanf("%d%d",&x,&y);

            add(x,y);

            add(y,x);

        }

        if(a>=b){

            if(qwq==){

                printf("%d\n",b);

            }

            else solve();

        }

        else{

            if(qwq==){

                printf("%d\n",a);

            }

            else dist();

        }

    }

}