#include <algorithm>
#include <iostream>
#include <string>

using namespace std;

int main() {
    const auto id = "aaabbb"s;
    
    for(string::const_iterator finish, start = cbegin(id); start != cend(id); start = finish) {
        finish = find_if(start, cend(id), [value = *start](const auto i) { return i != value; } );
        
        cout << distance(start, finish) << *start;
    }
}