// Enjoy your stay.

#include <bits/stdc++.h>

#define long long long
#define LOOPVAR_TYPE long

#define all(x) (x).begin(), (x).end()
#define sz(x) ((LOOPVAR_TYPE)(x).size())
#define foreach(it, X) for(__typeof((X).begin()) it = (X).begin(); it != (X).end(); it++)
#define GET_MACRO(_1, _2, _3, NAME, ...) NAME
#define _rep(i, n) _rep2(i, 0, n)
#define _rep2(i, a, b) for(LOOPVAR_TYPE i = (LOOPVAR_TYPE)(a); i < (LOOPVAR_TYPE)(b); i++)
#define rep(...) GET_MACRO(__VA_ARGS__, _rep2, _rep)(__VA_ARGS__)

#define fir first
#define sec second
#define mp make_pair
#define mt make_tuple
#define pb push_back

const double EPS = 1e-9;
const double PI = acos(-1.0);
const long INF = 1070000000LL;
const long MOD = 1000000007LL;

using namespace std;

typedef istringstream iss;
typedef stringstream sst;
typedef pair<LOOPVAR_TYPE, LOOPVAR_TYPE> pi;
typedef vector<LOOPVAR_TYPE> vi;

int n;
double p0,p1,p2;
double dp[22][16];

double f(int cur, int len){
	double& res=dp[cur][len];
	if(res > -1) return res;
	if(cur == n) return res = len;
	if(len == 0) return res = 0;
	res = 0;
	if(len == 1){
		res = p0 * 0 + (1-p0) * f(cur+1,len);
	}
	else rep(mask,1<<len){
		double sum = 0;
		double prob = 1;
		int combo = 0;
		rep(i,len+1){
			if(mask>>i&1){
				// survive
				if(i == 0 || i == len-1){
					prob *= 1-p1;
				}else prob *= 1-p2;
				combo++;
			}else{
				// die
				if(i == 0 || i == len-1){
					prob *= p1;
				}else if(i != len) prob *= p2;
				if(combo > 0){
					sum += f(cur+1,combo);
				}
				combo = 0;
			}
		}
		res += sum * prob;
	}
	return res;
}

int main(){
	cin.tie(0);
	ios_base::sync_with_stdio(0);
	
	cin>>n>>p0>>p1>>p2;
	n = 80 - n;
	p0 /= 100;
	p1 /= 100;
	p2 /= 100;
	rep(i,n+1)rep(j,15)dp[i][j] = -2;
	cout<<setprecision(16)<<f(0,14)*2<<endl;
}