#include<bits/stdc++.h>
using namespace std;
#define db double
const int N = 1e6+9;

char s[10];
int a[N],n;
bool cmp(int x,int y){
    return abs(x)<abs(y);
}
double fpr(db tp,db fp,db tn,db fn){
    if(tn+fp==0) return 1;
    return fp/(tn+fp);
}
double tpr(db tp,db fp,db tn,db fn){
    if(tp+fn==0) return 1;
    return tp/(tp+fn);
}
int m;
struct pp{db ff,tt;}b[N];
bool cmpp(pp x,pp y){
    return x.ff==y.ff?(x.tt>y.tt):(x.ff<y.ff);
}
int main(){
    scanf("%d",&n);int cnt=0;
    for(int i=1;i<=n;i++){
        scanf("%s%d",s,&a[i]);
        if(s[0]=='-') a[i]=-a[i],cnt++;
    }
    sort(a+1,a+n+1,cmp);
    double tp=n-cnt,fp=cnt,tn=0,fn=0;
    m=0;b[++m]=(pp){fpr(tp,fp,tn,fn),tpr(tp,fp,tn,fn)};
        // printf("%.8lf %.8lf\n",b[m].ff,b[m].tt);
    for(int i=1;i<=n;i++){
        if(a[i]<0) tn++,fp--;
        if(a[i]>0) tp--,fn++;
        while(i<n&&abs(a[i+1])==abs(a[i])){
            i++;
            if(a[i]<0) tn++,fp--;
            if(a[i]>0) tp--,fn++;
        }
        // printf("%lf %lf %lf\n",fp,tn,fp);
        b[++m]=(pp){fpr(tp,fp,tn,fn),tpr(tp,fp,tn,fn)};
        // printf("%.8lf %.8lf\n",b[m].ff,b[m].tt);
    }
    sort(b+1,b+m+1,cmpp);
    b[++m]=(pp){1,0};
    double ans=0,c=0;
    for(int i=1;i<=m;i++){
        ans+=c*(b[i].ff-b[i-1].ff);
        c=max(c,b[i].tt);
    }
    printf("%.14lf\n",ans);
    return 0;
}