решение при d = 0

#include <fstream>
#include <vector>
#include <string>
#include <cmath>
#include <algorithm>

using namespace std;

int main() {
	ifstream in("input.txt");
	ofstream out("output.txt");
	int d, n, res;
	double v, d_res = 0;
	in >> v >> d >> n;
	vector<int> x(n), time(n);
	string t;
	for (int i = 0; i < n; i++) {
		in >> x[i] >> t;
		time[i] += ((int)t[0] - 48) * 600 + ((int)t[1] - 48) * 60 + ((int)t[3] - 48) * 10 + ((int)t[4] - 48);
	}
	if (d == 0) {
		d_res += max((double)time[n-1], x[n - 1] / v);
		for (int i = n - 2; i >= 0; i--) {
			d_res = max((double)time[i], d_res + (double)(x[i + 1] - x[i]) / v);
		}
		d_res += (double)x[0] / v;
	}
	else {

	}
	res = ceil(d_res);
	out << res / 600;
	res %= 600;
	out << res / 60 << ":";
	res %= 60;
	out << res / 10;
	res %= 10;
	out << res;
}