#include<bits/stdc++.h>
#define fastio 	ios::sync_with_stdio(0); cin.tie(0); cout.tie(0);
#define endl "\n"
#define int long long int
using namespace std;
int mod = 1e9 + 7;

int32_t main() {
#ifndef ONLINE_JUDGE
	freopen("input.txt", "r", stdin);
	freopen("output.txt", "w", stdout);
#endif
	fastio;


	int n, x, t;
	cin >> n >> x >> t;
	int count = t, orig = x;
	while (x < n) {
		count += t;
		x += orig;
	}
	cout << count;
	return 0;
}
/*input
1000 1 1000
*/
 
#include <iostream>
#include <iomanip>
#include <string>
#include <vector>
#include <algorithm>
#include <sstream>
#include <queue>
#include <deque>
#include <bitset>
#include <iterator>
#include <list>
#include <stack>
#include <map>
#include <set>
#include <functional>
#include <numeric>
#include <utility>
#include <limits>
#include <climits>
#include <time.h>
#include <math.h>
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <assert.h>
#include <stdint.h>
#include <tgmath.h>
 
using namespace std;
 
/*******  All Required define Pre-Processors and typedef Constants *******/
#define ar array
#define scd(t) scanf("%d",&t)
#define scld(t) scanf("%ld",&t)
#define sclld(t) scanf("%lld",&t)
#define scc(t) scanf("%c",&t)
#define scs(t) scanf("%s",t)
#define scf(t) scanf("%f",&t)
#define sclf(t) scanf("%lf",&t)
#define rep(i, n) for (int i = 0; i < (n); i++)
#define FOREACH(it, l) for (auto it = l.begin(); it != l.end(); it++)
#define tests int r; cin >> r; while(r--)
#define MP make_pair
#define PI acos(-1)
typedef pair<long long, long long> PII;
typedef pair<double, double> PDD;
typedef vector<int> VI;
typedef vector<string> VS;
typedef vector<PII> VII;
typedef vector<VI> VVI;
typedef map<int,int> MPII;
typedef set<int> SETI;
typedef multiset<int> MSETI;
typedef long int int32;
typedef unsigned long int uint32;
typedef long long int int64;
typedef unsigned long long int  uint64;
#define godspeed ios_base::sync_with_stdio(false); cin.tie(NULL); cout.tie(0);
 
#define M(x) ((x)%(1000000007))
 
vector<int> adj_list[100010];
bool visited[10010];

void dfs(int node){
	visited[node] = true;
	for(int n: adj_list[node]){
		if(!visited[n]){
			dfs(n);
		}
	}
}



int main() {
 	int n;
 	int x;
 	int t;
 	cin>>n>>x>>t;
 	int ans = ceil(n*1.0/x)*t;

 	cout<<ans<<endl;
}



 
