//#pragma GCC optimize(3,"Ofast","inline")
//#pragma GCC optimize("-Ofast","-funroll-all-loops")
#include<bits/stdc++.h>
//#define getchar nc
#define sight(c) ('0'<=c&&c<='9')
#define LL long long
#define debug(a) cout<<#a<<" is "<<a<<"\n"
#define dput(a) puts("a")
#define eho(x) for(int i=head[x];i;i=net[i])
#define fi first
#define se second
inline char nc(){
static char buf[1000000],*p1=buf,*p2=buf;
return p1==p2&&(p2=(p1=buf)+fread(buf,1,1000000,stdin),p1==p2)?EOF:*p1++;
}
template <class T>
inline void read(T &x){// unsigned
    static char c;
    for (c=getchar();!sight(c);c=getchar());
    for (x=0;sight(c);c=getchar())x=x*10+c-48;
}
template <class T> void write(T x){if (x<10) {putchar('0'+x); return;} write(x/10); putchar('0'+x%10);}
template <class T> inline void writeln(T x){ if (x<0) putchar('-'),x*=-1; write(x); putchar('\n'); }
template <class T> inline void writel(T x){ if (x<0) putchar('-'),x*=-1; write(x); putchar(' '); }
using namespace std;
double solve(int x,double p){
	return x*p;
}
int n,l,r;
double p;
signed main() {
	#ifdef LOCAL
	//	freopen("test.in", "r", stdin);
	//	freopen("test.out", "w", stdout);
	#endif
	scanf("%d%lf%d%d",&n,&p,&l,&r);
	printf("%.10lf",solve(r,p)-solve(l-1,p)); 
    return 0;
}