//
//  main.cpp
//  dance
//
//  Created by Yg on 2024/4/26.
//
#include <iostream>
//#include <stdio.h>
#include <math.h>
#include <cmath>
#include <string.h>
#include <algorithm>
#include <queue>
#include <vector>
#include <stack>
#include <fstream>
#include <string>
#include <map>
#include <unordered_map>
using namespace std;
#define int long long

#define il inline

#define rd read()


il int read() {
    int res = 0, f = 1;
    char c = getchar();
    while (c < '0' || c > '9') {
        if (c == '-')
            f = -1;
        c = getchar();
    }
    while (c >= '0' && c <= '9') {
        res = res * 10 + c - '0';
        c = getchar();
    }
    return res * f;
}

signed main() {
    double a, k, l, r;
    cin >> a >> k >> l >> r;
    int x1, x2;
    x1 = ceil((l - a) / k);
    x2 = floor((r - a) / k);
    if (x1 <= x2)
        printf("%lld\n", x2 - x1 + 1);
    else
        printf("0\n");

    return 0;
}