#include<bits/stdc++.h>
#define int long long
#define mod 998244353ll
#define pb push_back
#define pii pair<int,int>
#define fi first
#define se second
#define mems(a,x) memset(a,x,sizeof(a))
using namespace std;
const int maxn=200010;
const int inf=1e18;
inline int read(){
	int x=0,fl=1;char ch=getchar();
	while(ch<'0'||ch>'9'){if(ch=='-')fl=-1;ch=getchar();}
	while(ch>='0'&&ch<='9'){x=(x<<3)+(x<<1)+(ch-'0');ch=getchar();}
	return x*fl;
}
bool mbe;

double n,p,l,r;
void work(){
	cin>>n>>p>>l>>r;
	printf("%.10lf\n",p*(r-l+1));
}

bool med;
int T;
signed main(){
	// freopen(".in","r",stdin);
	// freopen(".out","w",stdout);
	
	// cerr<<(&mbe-&med)/1024.0/1024.0<<"\n";
	
	T=1;
	while(T--)work();
}