#include <iostream>

#include <cstdio>

#include <cstring>

#include <cmath>

#include <algorithm>

#define Mod 1000000007

using namespace std;

#define N 2007

char mp[][][];

int G[][],from[];

int n,m,res,id,k,w;

int vis[],len[];

struct Ans

{

    int ind,pre;

}ans[];

int min(int ka,int kb)

{

    if(ka < kb)

        return ka;

    return kb;

}

int dif(char a[][],char b[][])

{

    int cnt = ;

    for(int i=;i<n;i++)

    {

        for(int j=;j<m;j++)

        {

            if(a[i][j] != b[i][j])

                cnt++;

        }

    }

    return cnt;

}

void Prim()

{

    int i,j,tag,mini;

    res = ;

    id = ;

    memset(vis,,sizeof(vis));

    memset(from,,sizeof(from));

    for(i=;i<=k;i++)

        len[i] = n*m;   //最大为n*m

    for(i=;i<=k;i++)

    {

        mini = Mod;

        for(j=;j<=k;j++)

        {

            if(!vis[j] && len[j] < mini)

            {

                mini = len[j];

                tag = j;

            }

        }

        if(mini == Mod)

            return;

        res += len[tag];

        if(len[tag] == n*m)

            ans[id].ind = tag,ans[id++].pre = ;

        else

            ans[id].ind = tag,ans[id++].pre = from[tag];

        vis[tag] = ;

        for(j=;j<=k;j++)

        {

            if(!vis[j] && len[j] > G[tag][j])

            {

                len[j] = G[tag][j];

                from[j] = tag;

            }

        }

    }

}

int main()

{

    int i,j;

    while(scanf("%d%d%d%d",&n,&m,&k,&w)!=EOF)

    {

        id = ;

        for(i=;i<=k;i++)

        {

            for(j=;j<n;j++)

                scanf("%s",mp[i][j]);

        }

        int T = n*m;

        for(i=;i<=k;i++)

        {

            for(j=i+;j<=k;j++)

                G[j][i] = G[i][j] = min(dif(mp[i],mp[j])*w,T);

            G[i][i] = ;

        }

        Prim();

        printf("%d\n",res);

        for(i=;i<id;i++)

            printf("%d %d\n",ans[i].ind,ans[i].pre);

    }

    return ;

}