#include <stdio.h>

int n;
int a[1000024];
int w[1000024];
int count = 0;
/*
int wtf(int i)
{
	w[i]++;
	count++;
	if (count >= 19997) {
		count -= 19997;
	}
	if (i == n - 1) {
		return a[i];
	}
	if (a[i] < wtf(i + 1)) {
		return a[i];
	}
	else {
		return wtf(i + 1);
	}
}*/

int main()
{
	FILE *fin = fopen("twoton.in", "r");
	FILE *fout = fopen("twoton.out", "w");
	fscanf(fin, "%d", &n);
	for (int i = 0; i < n; ++i) {
		fscanf(fin, "%d", &a[i]);
	}
	//wtf(0);
	count = 1;
	w[0] = 1;
	for (int i = 1; i < n; i++)
	{
		w[i] = 2 * w[i - 1];
		count += w[i];
		count %= 1997;
	}
	fprintf(fout, "%d\n", count);
	fclose(fin);
	fclose(fout);
}