#include<iostream>

#include<cstdio>

#include<cstring>

#include<string.h>

#include<algorithm>

#include<vector>

#include<cmath>

#include<stdlib.h>

#include<time.h>

#include<stack>

#include<set>

#include<map>

#include<queue>

using namespace std;

#define rep0(i,l,r) for(int i = (l);i < (r);i++)

#define rep1(i,l,r) for(int i = (l);i <= (r);i++)

#define rep_0(i,r,l) for(int i = (r);i > (l);i--)

#define rep_1(i,r,l) for(int i = (r);i >= (l);i--)

#define MS0(a) memset(a,0,sizeof(a))

#define MS1(a) memset(a,-1,sizeof(a))

#define MSi(a) memset(a,0x3f,sizeof(a))

#define inf 0x3f3f3f3f

#define lson l, m, rt << 1

#define rson m+1, r, rt << 1|1

typedef pair<int,int> PII;

#define A first

#define B second

#define MK make_pair

typedef __int64 ll;

template<typename T>

void read1(T &m)

{

    T x=,f=;char ch=getchar();

    while(ch<''||ch>''){if(ch=='-')f=-;ch=getchar();}

    while(ch>=''&&ch<=''){x=x*+ch-'';ch=getchar();}

    m = x*f;

}

template<typename T>

void read2(T &a,T &b){read1(a);read1(b);}

template<typename T>

void read3(T &a,T &b,T &c){read1(a);read1(b);read1(c);}

template<typename T>

void out(T a)

{

    if(a>) out(a/);

    putchar(a%+'');

}

int T,kase = ,i,j,k,n,m;

int dp[],a[],p[],tmp[];

int main()

{

    MSi(dp);

    int l,s,t;

    read1(l);

    read3(s,t,m);

    rep1(i,,m) read1(a[i]);

    if(s == t){

        int ans = ;

        rep1(i,,m) if(a[i]%s == ) ans++;

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

        return ;

    }

    sort(a,a+m+);

    a[] = ,a[++m] = l;

    rep1(i,,m){

        tmp[i] = tmp[i-] + (a[i] - a[i-])%;//递推实现离散化距离

        p[tmp[i]] = ;

    }

    rep1(i,s,t) dp[i] = p[i];

    rep1(i,*s,tmp[m]){ //这边从2*s开始

        int L = max(i-t,), r = i - s;

        rep1(j,L,r) dp[i] = min(dp[i],dp[j]);

        if(p[i]) dp[i]++;

    }

    printf("%d\n",dp[tmp[m]]-);//设置了L处也有石头

    return ;

}