/*
Given a sorted array consisting of 0s and 1s only, find the index of the first 1. If there’s no 1 present in the array, return -1

Input format
There are 2 lines of input

First line will contain a single integer n.

Next line will contain n space separated integers.

Output format
Print the index of first occuring if present, otherwise print -1.

Sample Input 1
4

0 0 1 1

Sample Output 1
2

Constraints
1<=n<=100000

0<=Ai<=1
*/

function getRequiredIndex(n,arr){
  let low = 0;
  let high = n - 1;
  while (low <= high) {
    let mid = Math.floor((low + high) / 2);
    if(arr[mid]==1)
    return mid;
    else if(1>arr[mid])
     low=mid+1;
     else
     high=mid-1;
  }
  return -1;
}

/**
 * @param {number} n
 * @param {number[]} arr
 * @return {number}
 */
function zeroOnes(n, arr) {
  let indexOfOne = getRequiredIndex(n, arr);
  /* console.log(indexOfOne) */
  if (indexOfOne == -1) return indexOfOne;
  while (indexOfOne >= 0 && arr[indexOfOne] === 1) indexOfOne--;
  return indexOfOne + 1;
}

function main() {
    let n = parseInt(readLine());
    let arr = readIntArr();

    let firstIndex = zeroOnes(n, arr);
    print(firstIndex);
}