Winter in Rodopi mountain

#include <cmath>
#include <cstdio>
#include <vector>
#include <iostream>
#include <algorithm>
#include <queue>
using namespace std;


int main() {
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);
    long unsigned int sum = 0;
    unsigned int rows, cols, days, rott_row, rott_col, rott_per_day = 0, rott_previous = 0;
    cin >> rows >> cols >> days;
    vector<vector<unsigned int>> grid(rows+1, vector<unsigned int>(cols+1));
    sum = rows*cols;
    queue <pair< unsigned int, unsigned int>> gps;
    while (cin >> rott_row >> rott_col) {
        grid[rott_row][rott_col] = 1;
        gps.push({ rott_row, rott_col });
        rott_per_day++;
        sum--;
    }

    for (unsigned int i = 0; i < days; i++)
    {
        rott_previous = rott_per_day;
        rott_per_day = 0;
        for (unsigned int j = 0; j < rott_previous; j++)
        {
            pair<unsigned int, unsigned int> cord = gps.front();
            unsigned int x = cord.first;
            unsigned int y = cord.second;
            if (x - 1 > 0 && grid[x - 1][y] != 1)         // Take the apple above the rotten (if there is one)
            {
                grid[x - 1][y] = 1;
                sum--;
                gps.push({ x-1, y });
                rott_per_day++;
            }
            if (x + 1 <= rows && grid[x + 1][y] != 1)         // Take the apple under the rotten (if there is one)
            {
                grid[x + 1][y] = 1;
                sum--;
                gps.push({ x+1, y });
                rott_per_day++;
            }
            if (y - 1 > 0 && grid[x][y - 1] != 1)         // Take the apple left the rotten (if there is one)
            {
                grid[x][y - 1] = 1;
                sum--;
                gps.push({ x, y-1 });
                rott_per_day++;
            }
            if (y + 1 <= cols && grid[x][y + 1] != 1)         // Take the apple right the rotten (if there is one)
            {
                grid[x][y + 1] = 1;
                sum--;
                gps.push({ x, y +1});
                rott_per_day++;
            }
            gps.pop();
        }

    }
    cout << sum;
    return 0;
}