#include <string>
#include <vector>
#include <iostream>
#include <algorithm>
#include <functional>
#include <string>
using namespace std;

int main(){
	long long v,t,p;
	cin >> v >> t >> p;
	unsigned long long ans=v*p+((v+(t-1))/t)*2+v;
	cout << ans << endl;
	
	return 0;
}