#include <bits/stdc++.h>
using namespace std;

#define IOS                  \
    ios::sync_with_stdio(0); \
    cin.tie(0);              \
    cout.tie(0);
#define endl "\n"
#define int long long
#define watch(x) cout << (#x) << " is " << (x) << endl;

int32_t main()
{
    IOS;

    int n, ans = 0;
    cin >> n;
    string s;
    cin >> s;

    for (char c = 'z'; c >= 'a'; c--)
    {
        for (int i = 0; i < s.size(); i++)

        {
            if (s[i] == c)
                if ((i > 0 && s[i] - 1 == s[i - 1]) || (i < s.size() - 1 && s[i] - 1 == s[i + 1]))
                {
                    s.erase(i, 1);
                    ans++;
                    i = i - 1;
                }
        }
    }
    cout << ans << endl;

    return 0;
}