Train schedule

input/code.cpp: In function 'void task5()':
input/code.cpp:18:14: error: 'sqrt' was not declared in this scope; did you mean 'sq'?
   18 |     int sq = sqrt(n) + 1;
      |              ^~~~
      |              sq

#include <iostream>
#include <algorithm>
#include <queue>
using namespace std;


void task5() {
    int n;
    cin >> n;
    vector<int> nums(n);

    for(int i = 0; i < n; i++) cin >> nums[i];

    vector<int> trainsNeeded(n, 0);
    vector<int> longInt;
    vector<int> startDay;

    int sq = sqrt(n) + 1;


    for(int i = 0; i < n; i++){
        if(nums[i] >= sq){
            longInt.push_back(nums[i]);
            startDay.push_back(i);
        }
    }


    vector<vector<int>> count(sq);
    for(int i = 0; i < n; i++){
        if(nums[i] < sq){
            count[nums[i]].push_back(i);
        }
    }


    for(int interval = 1; interval < sq; interval++){
        for(int start : count[interval]){
            for(int day = start; day < n; day += interval){
                trainsNeeded[day]++;
            }
        }
    }


    for(size_t i = 0; i < longInt.size(); i++){
        for(int j = startDay[i]; j < n; j += longInt[i]){
            trainsNeeded[j]++;
        }
    }


    for(int i = 0; i < n; i++){
        cout << trainsNeeded[i] << " ";
    }
    cout << endl;
}







void task4(){
    int n; 
    cin >> n;

    for(int i = 0; i < n; i++){
        for(int j = 0; j < n; j++){
            for(int k = 0; k < n; k++){
                if((k + j + i) % 3 == 0) 
                   cout << "R" << " ";
                else if((k+j +i) % 3 == 1)
                    cout << "G" << " ";
                else
                    cout << "B" << " ";
            }
            cout << endl;
        }
    }
}
int main() {
    

task5();
    return 0;

}