Count Substrings Starting and Ending with One

Given a binary string S of length N, your task is to count the number of substrings that start and end with the character '1'. A substring is a contiguous sequence of characters within the string. Note that every occurrence of '1' by itself is considered a valid substring.

The final answer can be computed using the formula:

\(\text{result} = \binom{c}{2} + c = \frac{c \times (c - 1)}{2} + c\)

where \(c\) is the total number of '1's in S.

Example: For S = "10101" and N = 5, the total number of valid substrings is 6.

inputFormat

The input consists of two lines:

1. The first line contains an integer N, representing the length of the binary string S.
2. The second line contains the binary string S composed of the characters '0' and '1'.

outputFormat

Output a single integer — the total number of substrings in S that start and end with '1'.

## sample

5
10101

6

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