#include <bits/stdc++.h>
#define ll long long
#define sti string
#define vt vector
#define INF ((int) 1e9)
#define MOD 1000000007
#define pii pair<int, int>
#define pil pair<int, ll>
#define pli pair<ll, int>
#define pll pair<ll, ll>
#define dbg(x) cerr << #x << " = " << x << '\n';
#define bit(mask, i) ((mask >> i) & 1)
#define fi first
#define sc second
#define MAXXTEST 100
#define MAXN 100000
#define MAXNTEST 100
#define SOTEST 100
using namespace std;
const sti name = "";
inline void stress_test ()
{
}
inline void file ()
{
freopen((name + ".inp").c_str(), "r", stdin);
freopen((name + ".out").c_str(), "w", stdout);
}
int main()
{
ios_base::sync_with_stdio(false);
cin.tie(nullptr); cout.tie(nullptr);
int H, W;
cin >> H >> W;
unordered_set<char> s;
char c;
for (int i = 1; i <= H * W; ++i)
{
cin >> c;
s.insert(c);
}
cout << s.size() - 1;
return 0;
}
