#include //ios::sync_with_stdio(false); //cin.tie(0); using namespace std; typedef long long ll; typedef unsigned long long ull; typedef pair pii; typedef pair ppii; typedef pair pipi; typedef pair pll; typedef pair ppll; typedef pair plpl; typedef tuple tl; ll mod=1000000007; ll mod2=998244353; ll mod3=1000003; ll inf=1000000000000000000; double pi=2*acos(0); #define rep(i,m,n) for(int i=m;i=m;i--) int dh[4]={1,-1,0,0}; int dw[4]={0,0,1,-1}; int ddh[8]={-1,-1,-1,0,0,1,1,1}; int ddw[8]={-1,0,1,-1,1,-1,0,1}; ll lmax(ll a,ll b){ if(a0){ if(k&1)ret*=now; now*=now; k/=2; } return ret; } int main(){ ios::sync_with_stdio(false); cin.tie(0); ll h,w,k;cin>>h>>w>>k; string s[h];rep(i,0,h)cin>>s[i]; int d[h+1][w+1][26]; rep(i,0,h+1){ rep(l,0,26)d[i][0][l]=0; } rep(i,0,w+1){ rep(l,0,26)d[0][i][l]=0; } rep(i,1,h+1){ rep(j,1,w+1){ rep(l,0,26){ d[i][j][l]=d[i-1][j][l]+d[i][j-1][l]-d[i-1][j-1][l]; } d[i][j][s[i-1][j-1]-'a']++; } } ll ans=0; if(k==1)ans=h+w-1; rep(i,0,h-1){ rep(j,0,w-1){ ll u=min(h-i,w-j)+1; ll dd=0; while(u-dd>1){ ll mid=(u+dd)/2; //if(i==0&&j==0)cout<0)cnt++; } if(cnt<=k)dd=mid; else u=mid; } ll cc=dd; u=dd+1; dd=0; while(u-dd>1){ ll mid=(u+dd)/2; int cnt=0; rep(l,0,26){ int b=d[i+mid][j+mid][l]-d[i+mid][j][l]-d[i][j+mid][l]+d[i][j][l]; if(b>0)cnt++; } if(cnt