#include <stdio.h>
int main(void){
  int n,a,b,c,x,y[100],i,cnt;
  while(1){
  BACK:
    scanf("%d %d %d %d %d",&n,&a,&b,&c,&x);
    if(!n)
      break;
    for(i=0;i<n;i++)
      scanf("%d",&y[i]);
    cnt=0;
    i=0;
    while(1){
      if(x==y[i])
	i++;
      if(i==n)
	break;
      x=(a*x+b)%c;
      cnt++;
      if(cnt>10000){
	puts("-1");
	goto BACK;
      }
    }
    printf("%d\n",cnt);
  }
  return 0;
}