#include<bits/stdc++.h>
#define int long long
#define pb push_back
#define fi first
#define se second
#define PII pair<int,int>
namespace IO {
    #define gh getchar
    inline int read(){char ch=gh();int x=0;bool t=0;while(ch<'0'||ch>'9')   t|=ch=='-',ch=gh();while(ch>='0'&&ch<='9') x=x*10+(ch^48),ch=gh();return t?-x:x;}
    inline char getc(){char ch=gh();while(ch<'a'||ch>'z') ch=gh();return ch;}
    inline void write(int x){if(x < 0){putchar('-');x = -x;}if(x > 9){write(x / 10);}putchar((x % 10 + '0'));}
}
using namespace IO;
using namespace std;
#define Tp template<typename T>
#define Ts template<typename T,typename... Ar>
namespace Debug{
	Tp void _debug(char* f,T t){cerr<<f<<'='<<t<<endl;}
	Ts void _debug(char* f,T x,Ar... y){while(*f!=',') cerr<<*f++;cerr<<'='<<x<<",";_debug(f+1,y...);}
	#ifdef LOCAL
	#define gdb(...) _debug((char*)#__VA_ARGS__,__VA_ARGS__)
	#else                                               
	#define gdb(...) void()
	#endif
}using namespace Debug;
const int Maxn = 1000010, mod = 1e9 + 7;
// vector<int> G[Maxn];
// int dep[Maxn];
// int mx, mid;
// void dfs(int u, int f){
//     dep[u] = dep[f] + 1;
//     if(dep[u] > mx) mx = dep[u], mid = u;
//     for(int v : G[u]){
//         if(v == f) continue;
//         dfs(v, u);
//     }
// }
signed main(){
    double p;
    int n, l, r;
    cin >> n >> p >> l >> r;
    printf("%.6f", (r - l + 1) * p);
}