#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#pragma GCC optimize("-Ofast")
//#pragma GCC optimize("trapv")
#pragma GCC target("sse,sse2,sse3,ssse3,sse4,sse4.2,popcnt,abm,mmx,avx2,tune=native")
#pragma GCC optimize("-ffast-math")
#pragma GCC optimize("-funroll-loops")
using namespace std;
using namespace __gnu_pbds;
#define vi vector<int>
#define vll vector<ll>
#define vii vector<pair<int, int>>
#define vvi vector<vi>
#define vvii vector<vii>
#define pii pair<int, int>
#define pll pair<ll, ll>
#define loop(_) for (int __ = 0; __ < (_); ++__)
#define forn(i, n) for (int i = 0; i < n; ++i)
#define pb push_back
#define f first
#define s second
#define sz(_) ((int)_.size())
#define all(_) _.begin(), _.end()
#define uni(_) unique(_)
#define lb lower_bound
#define ub upper_bound
#define si set<int>
#define ms multiset<int>
#define qi queue<int>
#define pq prioriry_queue<int>
#define mi map<int, int>
#define inc(i, l, r) for (int i = l; i <= r; i++)
#define dec(i, l, r) for (int i = l; i >= r; i--)
using lll = __int128;
using ll = long long;
using ld = long double;
const int N = 1e5 + 7;
const ll mod = 1e9 + 7;
const ll inf = 2e18;
auto ra = [] {char *p = new char ; delete p ; return ll(p) ; };
mt19937_64 rng(chrono::steady_clock::now().time_since_epoch().count() * (ra() | 1));
typedef tree<pii, null_type, less<pii>, rb_tree_tag, tree_order_statistics_node_update> os;
__int128 read()
{
__int128 x = 0, f = 1;
char ch = getchar();
while (ch < '0' || ch > '9')
{
if (ch == '-')
f = -1;
ch = getchar();
}
while (ch >= '0' && ch <= '9')
{
x = x * 10 + ch - '0';
ch = getchar();
}
return x * f;
}
void print(__int128 x)
{
if (x < 0)
{
putchar('-');
x = -x;
}
if (x > 9)
print(x / 10);
putchar(x % 10 + '0');
}
bool cmp(__int128 x, __int128 y) { return x > y; }
int n, m;
int main()
{
ios_base::sync_with_stdio(0);
cin.tie(0);
set<char> st;
cin >> n >> m;
loop(n * m)
{
char c;
cin >> c;
st.insert(c);
}
cout << sz(st) - 1;
return 0;
}
