AC

#include <iostream>
#include <vector>
#include <algorithm>

int LIS(std::vector<int> &v) {
    if (v.size() == 0) {
        return 0;
    }

    std::vector<int> tail(v.size(), 0);
    int length = 1;

    tail[0] = v[0];
    for (size_t i = 1; i < v.size(); i++) {
        if (v[i] < tail[0]) {
            tail[0] = v[i];
        } else if (v[i] > tail[length-1]) {
            tail[length++] = v[i];
        } else {
            tail[std::lower_bound(tail.begin( ), tail.begin( ) + length, v[i]) - tail.begin( )] = v[i];
        }
    }

    return length;
}

int main() {
    std::string cad;
    std::cin >> cad;
    std::vector<int> v;
    for (int i = 0; i < cad.size( ); ++i) {
        v.emplace_back(cad[i] - 'a');
    }
    std::cout << 26 - LIS(v) << '\n';
}