/*
ID: agageld1
LANG: C++17
TASK:
*/
#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define N 400005
#define ff first
#define ss second
#define pb push_back
#define sz(s) (int)s.size()
#define rep(c, a, b) for(c = a; c <= b; c++)
//mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
ll n, m, ans = 0;
char a[5000][5000];
map <char,int> vis;
int main () {
//freopen("txt.in","r",stdin);
//freopen("txt.out","w",stdout);
ios::sync_with_stdio(0);cin.tie(0);
cin >> n >> m;
for(int i= 1;i<=n;i++) {
for(int j =1;j<=m;j++) {
cin >> a[i][j];
if(!vis[a[i][j]]) ans++;
vis[a[i][j]] = 1;
}
}
cout << ans - 1 << '\n';
}
