#include <iostream>
#define REP(i,a,b) for(int i = (a); i < (b); i++)
#define rep(i,a) REP(i,0,a)
using namespace std;

int A;
double P0,P1,P2,U[20][14];

int main(void){
    cin >> A;
    cin >> P0 >> P1 >> P2;
    P0 /= 100.0, P1 /= 100.0, P2 /= 100.0;
    P0 = 1.0-P0, P1 = 1.0-P1, P2 = 1.0-P2;

    rep(i,14) U[0][i] = 1.0;
    
    REP(i,1,80-A+1) {
        U[i][ 0] = (P1*U[i-1][ 1] + P0*(1.0-U[i-1][ 1])) * U[i-1] [0];
        U[i][13] = (P1*U[i-1][12] + P0*(1.0-U[i-1][12])) * U[i-1][13];
        REP(j, 1, 13) {
            U[i][j] = (P2 * U[i-1][j-1]*U[i-1][j+1] + 
                       P1 * (U[i-1][j-1]*(1.0-U[i-1][j+1]) + (1.0-U[i-1][j-1])*U[i-1][j+1]) +
                       P0 * (1.0-U[i-1][j-1])*(1.0-U[i-1][j+1])) * U[i-1][j];
        }
    }

    double ans = 0.0;
    rep(i,14) ans += 2*U[80-A][i];
    printf("%.10f",ans);
}