#include<bits/stdc++.h>
#define ll long long
#define ull unsigned long long
#define pii pair<ll,int>
#define fi first
#define se second
#define mk make_pair
using namespace std;
ll read(){
    ll X = 0 ,r = 1;
    char ch = getchar();
    while(!isdigit(ch) && ch != '-') ch = getchar();
    if(ch == '-') r = -1,ch = getchar();
    while(isdigit(ch)) X = X*10+ch-'0',ch = getchar();
    return X*r;
}
int n,l,r;
double p;
int main(){
    cin >> n >> p >> l >> r;
    printf("%.10lf",(r-l+1)*p);
    return 0;
}