Bit string

#include <iostream>
#include <cmath>
#include <algorithm>
#include <stack>
#include <queue>
#include <vector>
#include <string>


using namespace std;

typedef long long LL;

const LL MAX = 500005;
const LL INF = (1000 * 1000 * 1000) + 9;

LL ans = 0, odd = 0, even = 0;
string input;

int main(void)
{
  getline(cin, input);
  LL n = input.size();
  for(LL i0 = 0; i0 < n; i0++)
  {
      if(input[i0] == '0')even++;
      else
      {
          LL temp = odd;
          odd = even;
          even = temp;
          odd++;
      }
      ans += even;
      // cout << odd << " " << even << endl;
  }
  cout << ans << endl;
  return 0;
}

Test 1

Group: 1

Verdict: ACCEPTED

Test 2

Group: 1

Verdict: ACCEPTED

Test 3

Group: 1

Verdict: ACCEPTED

Test 4

Group: 1

Verdict: ACCEPTED

Test 5

Group: 1

Verdict: ACCEPTED

Test 6

Group: 1

Verdict: ACCEPTED

Test 7

Group: 1

Verdict: ACCEPTED

Test 8

Group: 2

Verdict: ACCEPTED

Test 9

Group: 2

Verdict: ACCEPTED

Test 10

Group: 2

Verdict: ACCEPTED

Test 11

Group: 2

Verdict: ACCEPTED

Test 12

Group: 2

Verdict: ACCEPTED

Test 13

Group: 2

Verdict: ACCEPTED

Test 14

Group: 2

Verdict: ACCEPTED

Test 15

Group: 3

Verdict: ACCEPTED

Test 16

Group: 3

Verdict: ACCEPTED

Test 17

Group: 3

Verdict: ACCEPTED

Test 18

Group: 3

Verdict: ACCEPTED

Test 19

Group: 3

Verdict: ACCEPTED

Test 20

Group: 3

Verdict: ACCEPTED

Test 21

Group: 3

Verdict: ACCEPTED