text: /*
  Rathin Bhargava
  IIIT Bangalore
  
  */
  #include<bits/stdc++.h>
  #define mt make_tuple
  #define mp make_pair
  #define pu push_back
  #define INF 1000000001
  #define MOD 1000000007
  #define ll long long int
  #define ld long double
  #define vi vector<int>
  #define vll vector<long long int>
  #define fi first
  #define se second
  #define pr(v) { for(int i=0;i<v.size();i++) { v[i]==INF? cout<<"INF " : cout<<v[i]<<" "; } cout<<endl;}
  #define t1(x)                cerr<<#x<<" : "<<x<<endl
  #define t2(x, y)             cerr<<#x<<" : "<<x<<" "<<#y<<" : "<<y<<endl
  #define t3(x, y, z)          cerr<<#x<<" : " <<x<<" "<<#y<<" : "<<y<<" "<<#z<<" : "<<z<<endl
  #define t4(a,b,c,d)          cerr<<#a<<" : "<<a<<" "<<#b<<" : "<<b<<" "<<#c<<" : "<<c<<" "<<#d<<" : "<<d<<endl
  #define t5(a,b,c,d,e)          cerr<<#a<<" : "<<a<<" "<<#b<<" : "<<b<<" "<<#c<<" : "<<c<<" "<<#d<<" : "<<d<<" "<<#e<<" : "<<e<<endl
  #define t6(a,b,c,d,e,f)          cerr<<#a<<" : "<<a<<" "<<#b<<" : "<<b<<" "<<#c<<" : "<<c<<" "<<#d<<" : "<<d<<" "<<#e<<" : "<<e<<" "<<#f<<" : "<<f<<endl
  #define GET_MACRO(_1,_2,_3,_4,_5,_6,NAME,...) NAME
  #define t(...) GET_MACRO(__VA_ARGS__,t6,t5, t4, t3, t2, t1)(__VA_ARGS__)
  #define _ cerr<<"here"<<endl;
  #define __ {ios::sync_with_stdio(false);cin.tie(NULL);cout.tie(NULL);}
  
  
  using namespace std;
  
  int main()
  {
    __;
    int n;
    cin>>n;
    string s;
    cin>>s;
    ll count = 0;
    for(int i=0;i<n;i++)
    {
      int a = s[i]-'0';
      if(a%2==0) count+=i+1;
    }
    cout<<count<<endl;
    return 0;
  }
  
  