#include <iostream>
#include <algorithm>
#include <iomanip>
#include <vector>
#include <queue>
#include <deque>
#include <set>
#include <map>
#include <tuple>
#include <cmath>
#include <numeric>
#include <functional>
#include <cassert>

#define debug_value(x) cerr << "line" << __LINE__ << ":<" << __func__ << ">:" << #x << "=" << x << endl;
#define debug(x) cerr << "line" << __LINE__ << ":<" << __func__ << ">:" << x << endl;

template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return 1; } return 0; }
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return 1; } return 0; }

using namespace std;
typedef long long ll;

template<typename T>
vector<vector<T>> vec2d(int n, int m, T v){
    return vector<vector<T>>(n, vector<T>(m, v));
}

template<typename T>
vector<vector<vector<T>>> vec3d(int n, int m, int k, T v){
    return vector<vector<vector<T>>>(n, vector<vector<T>>(m, vector<T>(k, v)));
}

template<typename T>
void print_vector(vector<T> v, char delimiter=' '){
    if(v.empty()) {
        cout << endl;
        return;
    }
    for(int i = 0; i+1 < v.size(); i++) cout << v[i] << delimiter;
    cout << v.back() << endl;
}

using T = tuple<ll, int, int, int>;
const ll inf = 1e18;

int main(){
    ios::sync_with_stdio(false);
    cin.tie(0);
    cout << setprecision(10) << fixed;
    int n, m; cin >> n >> m;
    auto a = vec2d(n, m, 0ll);
    for(int i = 0; i < n; i++){
        for(int j = 0; j < m; j++){
            cin >> a[i][j];
        }
    }
    priority_queue<T, vector<T>, greater<T>> que;
    auto dist = vec3d(n, m, 2, inf);
    auto set_dist = [&](int i, int j, int k, ll d){
        if(chmin(dist[i][j][k], d)) que.push(T(d, i, j, k));
    };
    set_dist(0, 0, 0, 0);
    while(!que.empty()){
        auto [d, i, j, k] = que.top(); que.pop();
        if(d != dist[i][j][k]) continue;
        if(k == 0){
            set_dist(i, j, k+1, d+a[i][j]);
        }
        if(k == 1){
            for(int di: {1}){
                int ii = i+di;
                if(ii < 0 || ii >= n) continue;
                set_dist(ii, j, 1, d+a[ii][j]);
            }
        }
        if(true){
            for(int dj: {-1, 1}){
                int jj = j+dj;
                if(jj < 0 || jj >= m) continue;
                set_dist(i, jj, 0, d);
            }
        }
    }
    ll ans = inf;
    for(int i = 0; i < m; i++){
        for(int k = 0; k < 2; k++){
            chmin(ans, dist[n-1][i][k]);
        }
    }
    cout << ans << endl;
}