Educational Codeforces Round 8 B. New Skateboard

#include <cstdio>
#include <string>
#include <iostream>
#include <algorithm>
#include <vector>
#include <queue>
#include <stack>
#include <set>
#include <map>
#include <string>
#include <math.h>
#include <stdlib.h>
#include <bitset>
using namespace std;
#define ll long long
int main()
{
    ll ans = 0,i,j,num,k;
    string s;
    cin>>s;
    int len = s.size();
    for(i=0;i<len;i++){
        num = s[i]-‘0‘;
        if(num%4==0)
            ans++;
    }
    //cout<<ans<<endl;
    if(len>=2){
    for(i=0;i<len-1;i++){
        num = (s[i] - ‘0‘)*10+(s[i+1]-‘0‘);
        if(num%4==0)
            ans++;
    }
    }
    //cout<<ans<<endl;
    if(len>=3){
        for(i=0;i<len-1;i++){
            num  = (s[i] - ‘0‘)*10+(s[i+1]-‘0‘);
            if(num%4==0){
                ans+=i;
            }
            //cout<<ans<<endl;
        }
    }
    cout<<ans<<endl;
}