#![allow(unused_imports)]
#![allow(non_snake_case)]
use std::cmp::*;
use std::collections::*;
use std::io::Write;

#[allow(unused_macros)]
macro_rules! debug {
    ($($e:expr),*) => {
        #[cfg(debug_assertions)]
        $({
            let (e, mut err) = (stringify!($e), std::io::stderr());
            writeln!(err, "{} = {:?}", e, $e).unwrap()
        })*
    };
}

fn main() {
    let v = read_vec::<usize>();
    let (h, w, k) = (v[0], v[1], v[2]);

    let mut grid = vec![];
    for i in 0..h {
        let chs = read::<String>()
            .chars()
            .map(|ch| ch.to_digit(36).unwrap() as usize - 10)
            .collect::<Vec<_>>();
        grid.push(chs);
    }

    let mut cum2d_vec = vec![CumulativeSum2D::new(w, h); 26];
    for y in 0..h {
        for x in 0..w {
            cum2d_vec[grid[y][x]].add(x, y, 1);
        }
    }
    for ref mut cum2d in cum2d_vec.iter_mut() {
        cum2d.build();
    }

    let criterion1 = |start_x: usize, start_y: usize, width: usize| -> bool {
        let mut found = 0;
        for ref cum2d in cum2d_vec.iter() {
            if cum2d.query(start_x, start_y, start_x + width, start_y + width) > 0 {
                found += 1;
            }
            if found > k {
                return false;
            }
        }
        found <= k
    };
    let criterion2 = |start_x: usize, start_y: usize, width: usize| -> bool {
        let mut found = 0;
        for ref cum2d in cum2d_vec.iter() {
            if cum2d.query(start_x, start_y, start_x + width, start_y + width) > 0 {
                found += 1;
            }
            if found > k - 1 {
                return false;
            }
        }
        found <= k - 1
    };

    let mut ans = 0;
    for y in 0..h {
        for x in 0..w {
            let max_width = min(h - y, w - x);
            let (lb2, _) = binary_search(0, max_width + 1, x, y, criterion2);
            let (lb1, _) = binary_search(lb2, max_width + 1, x, y, criterion1);
            // debug!(x, y, lb1, lb2, max_width);
            ans += lb1 - lb2;
        }
    }
    println!("{}", ans);
}

fn read<T: std::str::FromStr>() -> T {
    let mut s = String::new();
    std::io::stdin().read_line(&mut s).ok();
    s.trim().parse().ok().unwrap()
}

fn read_vec<T: std::str::FromStr>() -> Vec<T> {
    read::<String>()
        .split_whitespace()
        .map(|e| e.parse().ok().unwrap())
        .collect()
}

#[derive(Clone)]
struct CumulativeSum2D {
    data: Vec<Vec<i32>>,
}

impl CumulativeSum2D {
    fn new(w: usize, h: usize) -> CumulativeSum2D {
        CumulativeSum2D {
            data: vec![vec![0; w + 1]; h + 1],
        }
    }

    fn add(&mut self, mut x: usize, mut y: usize, z: i32) {
        x += 1;
        y += 1;
        if x >= self.data[0].len() || y >= self.data.len() {
            return;
        }
        self.data[y][x] += z;
    }

    fn build(&mut self) {
        for i in 1..self.data.len() {
            for j in 1..self.data[i].len() {
                self.data[i][j] +=
                    self.data[i][j - 1] + self.data[i - 1][j] - self.data[i - 1][j - 1];
            }
        }
    }

    // sum of [sx, gx), [sy, gy)
    fn query(&self, sx: usize, sy: usize, gx: usize, gy: usize) -> i32 {
        self.data[gy][gx] - self.data[gy][sx] - self.data[sy][gx] + self.data[sy][sx]
    }
}

fn binary_search<F>(
    lb: usize,
    ub: usize,
    start_x: usize,
    start_y: usize,
    criterion: F,
) -> (usize, usize)
where
    F: Fn(usize, usize, usize) -> bool,
{
    let mut ok = lb;
    let mut ng = ub;
    while ng - ok > 1 {
        let mid = (ng + ok) / 2;
        if criterion(start_x, start_y, mid) {
            ok = mid;
        } else {
            ng = mid;
        }
    }
    (ok, ng)
}