#include<stdio.h>
int a[100];
int sum(int i, int j);
void main()
{int n,i,s[100],sum;
scanf("%d",&n);
for(i=0;i<n;i++)
scanf("%d",&a[i]);
printf("%d\n",sum(0,n-1));
}
int sum(int i, int j)
{
int d;
if(i==j)return a[i];
d=(i+j)/2;
return sum(i,d)+sum(d+1,j);
}