#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



//
//
//


void solve()
{
	double n,p,l,r;
	cin>>n>>p>>l>>r;
	printf("%.6lf",(r-l+1)*p);	
}
signed main()
{
	int _=1;
	while(_--)
		solve();
	return 0;
}