#include<stdio.h>
#include<stdlib.h>
#include<math.h>
#include<string.h>
#define REP(i,a,b) for(i=a;i<b;i++)
#define rep(i,n) REP(i,0,n)

#define M 103

int VA, VB, SA, SB, MA;
double dp[6][211][211], sum[6][211][211];

int main(){
  int i,j,k;
  double a, b, c;
  double per;

  scanf("%d%d%d%d%d", &VA, &VB, &SA, &SB, &MA);

  per = 1.0 / (SA+1) / (SB+1);

  a = 0; b = 1;
  while(b-a > 1e-6){
    c = (a+b)/2;

    rep(k,MA+1){
      rep(i,211) sum[k][0][i] = sum[k][i][0] = 0;
      REP(i,-M,VA+1) REP(j,-M,VB+1){
        sum[k][M+i+1][M+j+1] = sum[k][M+i][M+j+1] + sum[k][M+i+1][M+j] - sum[k][M+i][M+j];
        
        if(i <= 0 && j <= 0){
          dp[k][M+i][M+j] = c;
        } else if(i <= 0){
          dp[k][M+i][M+j] = 0;
        } else if(j <= 0){
          dp[k][M+i][M+j] = 1;
        } else {
          dp[k][M+i][M+j] = sum[k][M+i+1][M+j+1] - sum[k][M+i-SB][M+j+1] - sum[k][M+i+1][M+j-SA] + sum[k][M+i-SB][M+j-SA];
          dp[k][M+i][M+j] *= per / (1 - per);
        }

        if(k && dp[k][M+i][M+j] < dp[k-1][M+(i+1)/2][M+(j+1)/2]) dp[k][M+i][M+j] = dp[k-1][M+(i+1)/2][M+(j+1)/2];
        sum[k][M+i+1][M+j+1] += dp[k][M+i][M+j];
      }
    }

    if(c < dp[MA][M+VA][M+VB]) a = c; else b = c;
  }

  printf("%.10f\n",(a+b)/2);

  return 0;
}