#include<bits/stdc++.h>
using namespace std;
#define f first
#define s second
#define pb push_back
#define int long long
typedef long long ll;
typedef pair<int,int> PII;
const int N=2e5+10,M=4e5+10,mod=6666623333;

int T;
int n,l,r;
double q;

void solve()
{
	cin>>n>>q>>l>>r;
	printf("%.6lf",q*(r-l+1));
}

signed main()
{
	ios::sync_with_stdio(false);
	cin.tie(0);
	cout.tie(0); 
	T=1;
	while(T--)
	{
		solve();
	}
	return 0;
}