#include <bits/stdc++.h>
#include <cmath>
//#include <ext/pb_ds/tree_policy.hpp>
//#include <ext/pb_ds/assoc_container.hpp>

#pragma GCC optimize("Ofast")
#pragma GCC optimize("O3")
#pragma GCC optimize("unroll-loops")
#define INF 0x3F3F3F3F

using namespace std;
//using namespace __gnu_pbds;

//template <class T> using Tree = tree<T,null_type,less<T>,rb_tree_tag,tree_order_statistics_node_update>;
typedef long long ll;


const ll mod = 1e9;
const int phash=3;
const ll modhash=1000000000000000003;

int ans=0;

void rec(string s,int pos,int val)
{
    if (pos==s.size() || s.size()==1)
    {
        ans=max(ans,val);
        return;
    }

    if (s[pos]-1==s[pos+1])
    {
        string t=s;
        t.erase(pos,1);
        rec(t,max(pos-1,0),val+1);
    }
    else
    if (pos>0 && s[pos]-1==s[pos-1])
    {
        string t=s;
        t.erase(pos,1);
        rec(t,max(pos-1,0),val+1);
    }

    rec(s,pos+1,val);
}
int main()
{
    //freopen("input.txt","r",stdin);
    //freopen("output.txt","w",stdout);
    ios_base::sync_with_stdio(false);

    int n;
    cin >> n;
    string s;
    cin >> s;

    //rec(s,0,0);

    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=-1;
            }
        }

    cout << ans;

}