public class Zero {
public static void main(String[] args) throws IOException {
BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
int K = Integer.parseInt(br.readLine());
int[] nums = new int[K];
int idx = 0;
for(int i = 0; i < K; i++) {
int num = Integer.parseInt(br.readLine());
if(num != 0) {
nums[idx++] = num;
} else {
nums[--idx] = 0;
}
}
System.out.println(Arrays.stream(nums).sum());
}
}