#include<bits/stdc++.h>
#define rep(i,a,b) for(int i=(a);i<=(b);i++)
#define per(i,a,b) for(int i=(a);i>=(b);i--)
#define sz(x) ((int)x.size())
#define ll long long
#define LL __int128
using namespace std;
using pii=pair<ll,ll>;
using tup=tuple<int,int,int>;
const int N=500005;
int n,o,s[N];
long double a[N],y[N],f[N];
int main(){
    scanf("%d",&n),a[0]=1;
    rep(i,1,n) scanf("%Lf",&a[i]);
    s[++o]=n,y[n]=(f[n]+n)*a[n];
    // per(i,n-1,0) rep(j,i+1,n) f[i]=max(f[i],(f[j]+j-i)*a[j]);
    per(i,n-1,0){
        int l=1,r=o-1,as=o;
        while(l<=r){
            int mid=(l+r)>>1;
            if(y[s[mid]]-i*a[s[mid]]>=y[s[mid+1]]-i*a[s[mid+1]]) as=mid,r=mid-1;
            else l=mid+1;
        }
        f[i]=y[s[as]]-i*a[s[as]];
        y[i]=(f[i]+i)*a[i];
        while(o>=2&&(y[i]-y[s[o]])/(a[i]-a[s[o]])>=(y[s[o]]-y[s[o-1]])/(a[s[o]]-a[s[o-1]])) o--;
        s[++o]=i;
    }
    printf("%.10Lf",f[0]);
}