#include <iostream>
#include <cstdio>
#include <string.h>
#include <algorithm>
#include <cmath>
#include <vector>
#include <queue>
#include <set>
#include <stack>
#include <string>
#include <map>#define max(x,y) ((x)>(y)?(x):(y))
#define min(x,y) ((x)<(y)?(x):(y))
#define abs(x) ((x)>=0?(x):-(x))
#define i64 long long
#define u32 unsigned int
#define u64 unsigned long long
#define clr(x,y) memset(x,y,sizeof(x))
#define CLR(x) x.clear()
#define ph(x) push(x)
#define pb(x) push_back(x)
#define Len(x) x.length()
#define SZ(x) x.size()
#define PI acos(-1.0)
#define sqr(x) ((x)*(x))
#define MP(x,y) make_pair(x,y)#define FOR0(i,x) for(i=0;i<x;i++)
#define FOR1(i,x) for(i=1;i<=x;i++)
#define FOR(i,a,b) for(i=a;i<=b;i++)
#define DOW0(i,x) for(i=x;i>=0;i--)
#define DOW1(i,x) for(i=x;i>=1;i--)
#define DOW(i,a,b) for(i=a;i>=b;i--)
using namespace std;void RD(int &x){scanf("%d",&x);}
void RD(i64 &x){scanf("%I64d",&x);}
void RD(u32 &x){scanf("%u",&x);}
void RD(double &x){scanf("%lf",&x);}
void RD(int &x,int &y){scanf("%d%d",&x,&y);}
void RD(i64 &x,i64 &y){scanf("%I64d%I64d",&x,&y);}
void RD(u32 &x,u32 &y){scanf("%u%u",&x,&y);}
void RD(double &x,double &y){scanf("%lf%lf",&x,&y);}
void RD(int &x,int &y,int &z){scanf("%d%d%d",&x,&y,&z);}
void RD(i64 &x,i64 &y,i64 &z){scanf("%I64d%I64d%I64d",&x,&y,&z);}
void RD(u32 &x,u32 &y,u32 &z){scanf("%u%u%u",&x,&y,&z);}
void RD(double &x,double &y,double &z){scanf("%lf%lf%lf",&x,&y,&z);}
void RD(char &x){x=getchar();}
void RD(char *s){scanf("%s",s);}
void RD(string &s){cin>>s;}void PR(int x) {printf("%d\n",x);}
void PR(i64 x) {printf("%I64d\n",x);}
void PR(u32 x) {printf("%u\n",x);}
void PR(double x) {printf("%.6lf\n",x);}
void PR(char x) {printf("%c\n",x);}
void PR(char *x) {printf("%s\n",x);}
void PR(string x) {cout<<x<<endl;}const int N=505;
int a[N][N],n,m,K,id,b[N][N];
int visit[N][N];
int dx[]={0,0,1,-1};
int dy[]={1,-1,0,0};int OK(int x,int y)
{return x>=1&&x<=n&&y>=1&&y<=m;
}int L,R,U,D;int DFS(int x,int y)
{visit[x][y]=1;U=min(U,x);D=max(D,x);L=min(L,y);R=max(R,y);int i,xx,yy,cnt=1;FOR0(i,4){xx=x+dx[i];yy=y+dy[i];if(OK(xx,yy)&&!visit[xx][yy]&&a[xx][yy]==a[x][y]){cnt+=DFS(xx,yy);}}a[x][y]=id;return cnt;
}int visit1[N][N];void DFS1(int x,int y,int t)
{visit1[x][y]=1;int i,xx,yy;FOR0(i,4){xx=x+dx[i];yy=y+dy[i];if(xx>=U&&xx<=D&&yy>=L&&yy<=R&&!visit1[xx][yy]&&a[xx][yy]!=t){DFS1(xx,yy,t);}}
}int main()
{RD(n,m,K);int i,j,k,p,q;clr(a,0);clr(a,-1);FOR1(i,n) FOR1(j,m) scanf("%1d",&a[i][j]);id=10;FOR1(i,n) FOR1(j,m) if(!visit[i][j]){L=U=n+m;R=D=0;id++;k=DFS(i,j);if(k<K) continue;L--; U--; R++; D++;clr(visit1,0);DFS1(U,L,a[i][j]);for(p=U+1;p<D;p++) for(q=L+1;q<R;q++){if(!visit1[p][q]){b[p][q]=1;}}}int ans=0;FOR1(i,n) FOR1(j,m) ans+=b[i][j];PR(ans);return 0;
}