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#define _CRT_SECURE_NO_WARNINGS
#include <stdio.h>
#include <string.h>
#include <ctype.h>
#include <stdlib.h>

typedef struct node_ {
	struct node_* l, * r;
	int val;
} node;

node* build() {
	node* x = (node*)malloc(sizeof(node));
	char c = getc(stdin);
	x->l = 0, x->r = 0;
	if (isdigit(c)) {
		ungetc(c, stdin);
		x->l = (node*)malloc(sizeof(node));
		x->l->r = 0; x->l->l = 0;
		scanf("%d", &x->l->val);
	}
	else
		x->l = build();
	while ((c = getc(stdin)) == ' ');
	if (c == EOF || c == '\n')
		return x->l;
	if (isdigit(c)) {
		ungetc(c, stdin);
		x->r = (node*)malloc(sizeof(node));
		x->r->r = 0; x->r->l = 0;
		scanf("%d", &x->r->val);
	}
	else
		x->r = build();
	getc(stdin);
	return x;
}

double solve(node* n) {
	if (!n) 
		return 0;
	int cnt = !!(n->l) + !!(n->r);
	if (!cnt) 
		return n->val;
	double sum = solve(n->l) + solve(n->r);
	return sum / cnt;
}

void freee(node* n) {
	if (!n) return;
	freee(n->l); freee(n->r);
	free(n);
}

signed main() {
	node* d = build();
	printf("%.2lf", solve(d));
	freee(d);
}