#include<bits/stdc++.h>
using namespace std;


#define li          long long int
#define rep(i,to)   for(li i=0;i<((li)(to));i++)
#define repp(i,start,to)    for(li i=(li)(start);i<((li)(to));i++)
#define pb          push_back
#define sz(v)       ((li)(v).size())
#define bgn(v)      ((v).begin())
#define eend(v)     ((v).end())
#define allof(v)    (v).begin(), (v).end()
#define dodp(v,n)       memset(v,(li)n,sizeof(v))
#define bit(n)      (1ll<<(li)(n))
#define mp(a,b)     make_pair(a,b)
#define rin rep(i,n)
#define EPS 1e-12
#define ETOL 1e-8
#define MOD 1000000007
typedef pair<li, li> PI;

#define INF bit(60)

#define DBGP 1


#define idp if(DBGP)
#define F first
#define S second
#define p2(a,b)     idp cout<<a<<"\t"<<b<<endl
#define p3(a,b,c)       idp cout<<a<<"\t"<<b<<"\t"<<c<<endl
#define p4(a,b,c,d)     idp cout<<a<<"\t"<<b<<"\t"<<c<<"\t"<<d<<endl
#define p5(a,b,c,d,e)       idp cout<<a<<"\t"<<b<<"\t"<<c<<"\t"<<d<<"\t"<<e<<endl
#define p6(a,b,c,d,e,f)     idp cout<<a<<"\t"<<b<<"\t"<<c<<"\t"<<d<<"\t"<<e<<"\t"<<f<<endl
#define p7(a,b,c,d,e,f,g)       idp cout<<a<<"\t"<<b<<"\t"<<c<<"\t"<<d<<"\t"<<e<<"\t"<<f<<"\t"<<g<<endl
#define p8(a,b,c,d,e,f,g,h)     idp cout<<a<<"\t"<<b<<"\t"<<c<<"\t"<<d<<"\t"<<e<<"\t"<<f<<"\t"<<g<<"\t"<<h<<endl
#define p9(a,b,c,d,e,f,g,h,i)       idp cout<<a<<"\t"<<b<<"\t"<<c<<"\t"<<d<<"\t"<<e<<"\t"<<f<<"\t"<<g<<"\t"<<h<<"\t"<<i<<endl
#define p10(a,b,c,d,e,f,g,h,i,j)        idp cout<<a<<"\t"<<b<<"\t"<<c<<"\t"<<d<<"\t"<<e<<"\t"<<f<<"\t"<<g<<"\t"<<h<<"\t"<<i<<"\t"<<j<<endl
#define foreach(it,v)   for(__typeof((v).begin()) it=(v).begin(); it!=(v).end(); ++it)
#define p2p(x)      idp p2((x).F, (x).S)
#define dump(x,n)   idp{rep(i,n){cout<<x[i]<<" ";}puts("");}
#define dump2(x,n)  idp{rep(i,n){cout<<"["<<x[i].F<<" , "<<x[i].S<<"] ";}puts("");}
#define dumpi(x)    idp{foreach(it, x){cout<<(*it)<<" ";}puts("");}
#define dumpi2(x)   idp{foreach(it, x){cout<<"["<<(it)->F<<" , "<<(it)->S<<"] ";}puts("");}

#define read2d(a,w,h)   rep(i,h)rep(j,w)cin>>a[i][j]
#define dump2d(a,w,h)   rep(i,h){rep(j,w)cout<<a[i][j]<<" ";puts("");}

typedef pair<li, li> PI;

string s[333];
li memo[333][333];
li h, w;

// [ずれ+300][ながさ]
li prec[633][333];

inline li sabun(li ha, li hb) {
    return prec[ha - hb + 300][min(ha, hb)];
}

inline li precalc(li x) {
    rep(i, h * 2 + 1) {
        li ha, hb;
        li ia, ib;
        if (i < h) {
            // bのが背が高い
            ha = i;
            hb = h;
            ia = 0;
            ib = (h - i);
        } else {
            // aのが背が高い
            ha = h;
            hb = h * 2 - i;
            ia = (i - h);
            ib = 0;
        }
        prec[i][0] = 0;
        rep(j, min(ha, hb)) {
            li judge = (s[ia + j][x] == s[ib + j][x + 1] ? 1 : 0);
            prec[300 - h + i][j + 1] = prec[300 - h + i][j] + judge;
        }
    }
}

li solve(li a, li b, li x) {
    if (memo[a][b] != INF)return memo[a][b];

    li res = INF;
    // a
    if (a > 0)
        res = min(res, sabun(a, b) + solve(a - 1, b, x));
    // b
    if (b > 0)
        res = min(res, sabun(a, b) + solve(a, b - 1, x));

    return (memo[a][b] = res);
}

inline li calc(li x) {
    // init
    rep(i, 333)rep(j, 333)memo[i][j] = INF;
    memo[0][0] = 0;
    // precalc
    precalc(x);
    return solve(h, h, x);
}

int main() {
    cin >> h >> w;
    rep(i, h) {
        cin >> s[i];
    }
    li res = 0;
    rep(i, w - 1) {
        res += calc(i);
    }
    cout << res << endl;
    return 0;
}

Measured memory_bytes: 2816