#include <stdio.h>
#include <stdlib.h>

#define MAXSIZE 500000

long n, k, auah, buah, i, x, y;

typedef struct {
    long source;
    long destination;
} pair;

pair v[MAXSIZE];
long sol[MAXSIZE];

void init() {
    long i;

    for (i = 0;i < n;i++)
        sol[i] = buah;
}

void swap(long *x, long *y) {
    long t = *x;

    *x = *y;
    *y = t;
}

long partition( pair a[], long l, long r) {
   long pivot, i, j;
   pair t;
   pivot = a[l].source;
   i = l; j = r+1;

   while( 1)
   {
   	do ++i; while( a[i].source <= pivot && i <= r );
   	do --j; while( a[j].source > pivot );
   	if( i >= j ) break;
   	t = a[i]; a[i] = a[j]; a[j] = t;
   }
   t = a[l]; a[l] = a[j]; a[j] = t;
   return j;
}

void quickSort( pair a[], long l, long r)
{
   long j;

   if( l < r )
   {
   	// divide and conquer
        j = partition( a, l, r);
       quickSort( a, l, j-1);
       quickSort( a, j+1, r);
   }

}

int main()
{
    pair d;

    scanf("%ld%ld%ld%ld", &n, &k, &auah, &buah);

    init();
    for (i = 0; i < k; i++) {
        scanf("%ld%ld", &x, &y);
        if (x > y)
            swap(&x, &y);
        d.source = x-1;
        d.destination = y-1;
        v[i] = d;
    }

    quickSort(v, 0, k-1);

    sol[0] = 0;
    for (i = 0; i < k; i++) {
        if (sol[v[i].source] + auah < sol[v[i].destination])
            sol[v[i].destination] = sol[v[i].source] + auah;
    }

    printf("%ld\n", sol[n-1]);
    return 0;
}