var GET=(function(){function f(s){return new g(s);}function g(s){this._s=s.trim().split("\n");this._y=0;}g.prototype.a=function(f){var s=this._s, y=this._y, r;if(typeof s[y]==="string")s[y]=s[y].split(" ").reverse();r=s[y].pop();if(!s[y].length)this._y++;return f?r:+r;};g.prototype.l=function(f){var s=this._s[this._y++].split(" ");return f?s:s.map(a=>+a);};g.prototype.m=function(n,f){var r=this._s.slice(this._y,this._y+=n).map(a=>a.split(" "));return f?r:r.map(a=>a.map(a=>+a));};g.prototype.r=function(n,f){var r=this._s.slice(this._y,this._y+=n);return f?r:r.map(a=>+a);};return f;})();
var o=GET(require("fs").readFileSync("/dev/stdin","utf8"));

console.log(main());
function main(){
  var n = o.a();
  var p = o.l();
  var dp = [1-p[0],p[0]];
  for(var i = 1; i < n; i++){
    dp[i+1] = dp[i] * p[i];
    for(var j = i; j > 0; j--){
      dp[j] = dp[j-1] * p[i] + dp[j] * (1 - p[i]);
    }
    dp[0] = dp[j] * (1 - p[i]);
  }
  var ans = 0;
  for(i = (n+1) / 2; i <= n; i++)ans += dp[i];
  return ans;
}