#include "stdio.h"
#include "malloc.h"

long num_min,bridge_len,*array,stone_sum;
int min,max;

int Search(long i)
{
long j;

for(j=0;j<stone_sum;j++)
if(array[j]==i)
return 1;
return 0;
}

void Frog_Jump(long i,long total)
{
int j;
long num;

for(j=min;j<=max;j++)
{
num=total+Search(i+j);
if( (i+j)<array[stone_sum-1] )
Frog_Jump(i+j,num);
if( (i+j)>=array[stone_sum-1] && num < num_min )
num_min=num;
}
}

int main()
{
long i;

printf("please input the length of bridge :\n");
scanf("%ld",&bridge_len);
printf("please input the range of frog :\n");
scanf("%d%d",&min,&max);
printf("please input the num of stone :\n");
scanf("%ld",&stone_sum);
array=(long *) malloc (sizeof(long)*stone_sum);
for(i=0;i<stone_sum;i++)
scanf("%ld",array+i);
num_min=stone_sum;
Frog_Jump(0,0);

printf("\n%ld\n",num_min);
free(array);
return 0;
}