#include<bits/stdc++.h>
using namespace std;
#define sf(x) scanf("%lld",&x)
#define sff(x,y) scanf("%lld%lld",&x,&y)
#define endl '\n'
#define IOS ios::sync_with_stdio(false);cin.tie(0);cout.tie(0)
#define pf(x) printf("%lld",x)
#define pii pair<int,int> 
#define f first 
#define s second
#define int long long



//
int  m,ll,rr;
double p,pp;
//
//


void solve()
{	
	cin>>m>>pp>>ll>>rr;
	p=1/pp;
	
	double res=1;
	int l = -1,r=m+1;
	while(l+1<r)
	{
		int mid  =l+r>>1;
		if(p*(double)mid>=ll) r=mid;
		else l=mid;
	}
	res-=r;
	
	l = -1,r=m+1;
	while(l+1<r)
	{
		int mid  =l+r>>1;
		if(p*(double)mid>rr) r=mid;
		else l=mid;
	}
	res+=l;
	
	cout<<max(0.0,res)<<endl;
}
signed main()
{
	IOS;
	int _=1;
	while(_--)
		solve();
	return 0;
}