#include <bits/stdc++.h>
#define ll long long
#define LL long long
#define ls p<<1
#define rs p<<1|1
#define Ma 1000005
#define mod 1000000007
#define PLL pair<ll,ll>
#define PDD pair<double,double>
#define IOS ios::sync_with_stdio(false);cin.tie(0);cout.tie(0);
#define fi first
#define se second
#define N 61
#define pb push_back
#define ld long double
#define all(x) x.begin(),x.end()
#define inf 1e18

using namespace std;
ld n,p,l,r;
ll a[Ma];

void sol()
{
	cin>>n>>p>>l>>r;
	printf("%.6Lf\n",(r-l+1)*p);
	
	return;
}

int main()
{
	IOS
	ll tt=1;
	//cin>>tt;
	while (tt--)
		sol();
	return 0;
}