#include #define rep(i,a,b) for(int i=a;i=b;i--) #define fore(i,a) for(auto &i:a) #define all(x) (x).begin(),(x).end() //#pragma GCC optimize ("-O3") using namespace std; void _main(); int main() { cin.tie(0); ios::sync_with_stdio(false); _main(); } typedef long long ll; const int inf = INT_MAX / 2; const ll infl = 1LL << 60; templatebool chmax(T& a, const T& b) { if (a < b) { a = b; return 1; } return 0; } templatebool chmin(T& a, const T& b) { if (b < a) { a = b; return 1; } return 0; } //--------------------------------------------------------------------------------------------------- template struct Ruisekiwa2D { int v[VH][VW]; Ruisekiwa2D() { rep(y, 0, VH) rep(x, 0, VW) v[y][x] = 0; } void set(int x, int y, int c) { v[y][x] = c; } void build() { rep(y, 0, VH) rep(x, 0, VW) { if (0 < y) v[y][x] += v[y - 1][x]; if (0 < x) v[y][x] += v[y][x - 1]; if (0 < y && 0 < x) v[y][x] -= v[y - 1][x - 1]; } } int get(int sx, int sy, int tx, int ty) { // [sx,sy]~[tx,ty] assert(sx <= tx && sy <= ty); int rs = v[ty][tx]; if (0 < sx) rs -= v[ty][sx - 1]; if (0 < sy) rs -= v[sy - 1][tx]; if (0 < sx && 0 < sy) rs += v[sy - 1][sx - 1]; return rs; } }; /*---------------------------------------------------------------------------------------------------             ∧_∧       ∧_∧  (´<_` )  Welcome to My Coding Space!      ( ´_ゝ`) /  ⌒i @hamayanhamayan     /   \    | |     /   / ̄ ̄ ̄ ̄/  |   __(__ニつ/  _/ .| .|____      \/____/ (u ⊃ ---------------------------------------------------------------------------------------------------*/ int H, W, K; string C[2010]; Ruisekiwa2D<2010, 2010> r2d[26]; //--------------------------------------------------------------------------------------------------- int get(int x, int y, int length) { int res = 0; rep(c, 0, 26) if (0 < r2d[c].get(x, y, x + length - 1, y + length - 1)) res++; return res; } //--------------------------------------------------------------------------------------------------- int binarySearch(int x, int y, int l, int r, int limit) { //[l,r) if (limit <= get(x, y, l)) return l; int ng = l, ok = r; while (ng + 1 != ok) { int md = (ng + ok) / 2; if (limit <= get(x, y, md)) ok = md; else ng = md; } return ok; } //--------------------------------------------------------------------------------------------------- void _main() { cin >> H >> W >> K; rep(y, 0, H) cin >> C[y]; rep(y, 0, H) rep(x, 0, W) r2d[C[y][x] - 'a'].set(x, y, 1); rep(c, 0, 26) r2d[c].build(); ll ans = 0; rep(y, 0, H) rep(x, 0, W) { int maxlen = min(W - x, H - y); ans += binarySearch(x, y, 1, maxlen + 1, K + 1) - binarySearch(x, y, 1, maxlen + 1, K); } cout << ans << endl; }