#include <stdio.h>

void main() {
    int digits;
    scanf("%d", &digits);

    if (digits < 9) {
        int result = 0;
        digits -= 1;

        while (digits >= 0) {
            int i = 1;
            int timer = 2;

            while (i < digits) {
                timer *= 2;
                i++;
            }

            if (digits == 0)
                timer -= 1;

            int temp;
            scanf("%d", &temp);

            result += temp * timer;
            digits--;
        }

        printf("%d", result);
    }
}