/*****************************************
Note  :
******************************************/
#include <queue>
#include <math.h>
#include <stack>
#include <stdio.h>
#include <iostream>
#include <vector>
#include <iomanip>
#include <string.h>
#include <algorithm>
#define int long long
#define IL inline
const int N = 1e6+10;
const int INF = 0x3f3f3f3f;
using namespace std;
IL int read()
{
    char ch = getchar();
    int f = 1, num = 0;
    while(ch>'9'||ch<'0')
    {
        if(ch=='-') f = -1;
        ch=getchar();
    }
    while(ch>='0'&&ch<='9')
        num = num*10+ch-'0', ch = getchar();
    return num*f;
}
int n,ans[N],tot;
struct node
{
	int num,id;
};
bool operator <(node a,node b)
{
	if(a.num!=b.num)
		return a.num>b.num;
	return a.id>b.id;
}
priority_queue<node> q;
signed main()
{
	n=tot=read();
	for(int i = 1;i<=n;i++)
		q.push({read(),i});
	while(!q.empty())
	{
		node x=q.top();
		q.pop();
		if(q.empty()) 
		{
			ans[x.id]=x.num;
			break;
		}
		node y=q.top();
		if(x.num==y.num)
		{
			q.pop(),tot--;
			q.push({x.num*2,y.id});
		}
		else
			ans[x.id]=x.num;
	}
	printf("%lld\n",tot);
	for(int i = 1;i<=n;i++)
		if(ans[i])
			printf("%lld ",ans[i]);
}