Revise paste Untitled

#include <iostream>
#include <vector>
using namespace std;

int main()
{
    vector<int>v;
    int n,m;
    cin>>n>>m;
    int mat[n][m];
    for(int i=0;i<n;i++)
    {
        for(int j=0;j<m;j++)
        {
            cin>>mat[i][j];
        }
    }
    for(int i = 0; i < n; i++) {
        for(int j = 0; j < m; j++) {
            int najmal_sosed = 2e9;
            if(i + 1 < n) {
                najmal_sosed = min(najmal_sosed, mat[i + 1][j]);
            }
            if(i - 1 >= 0) {
                najmal_sosed = min(najmal_sosed, mat[i - 1][j]);
            }
            if(j + 1 < m) {
                najmal_sosed = min(najmal_sosed, mat[i][j + 1]);
            }
            if(j - 1 >= 0) {
                najmal_sosed = min(najmal_sosed, mat[i][j - 1]);
            }
            if(najmal_sosed > mat[i][j]) {
                v.push_back(najmal_sosed - mat[i][j]);
            }
        }
    }
    if(v.size() == 0) {
        cout << -1 << endl;
    }
    else{
        sort(v.begin(), v.end());
        for(int i = v.size() - 1; i>=0;i--){
            cout <<v[i] << " ";
        }
    }
    
    return 0;
}