#include <iostream>
#include <string>
#include <algorithm>
#include <vector>
#include <stack>
#include <queue>
#include <list>
#include <set>
#include <map>
#include <numeric>
#include <regex>
#include <tuple>
#include<iomanip>
using namespace std;

typedef long long ll;
typedef pair<int, int> P;
#define MOD 1000000007 // 10^9 + 7
#define INF 1000000000 // 10^9
#define LLINF 1LL<<60

ll A, B, C;

// 10^k <= n < 10^k+1
int digit(ll n) {
	int res = 0;
	while (n > 0) {
		n /= 10;
		res++;
	}
	return res - 1;
}

// n年までにもらえる総額がCより多いかどうか
bool money(ll n) {
	if (digit(n / A) + digit(B) >= 18) return true;
	else {
		ll tmp = (n / A)*B + n - (n / A);
		return tmp >= C;
	}
}


int main() {
	cin.tie(0);
	ios::sync_with_stdio(false);

	cin >> A >> B >> C;

	// left < ans <= right
	ll left = -1;
	ll right = C;
	while (left + 1 != right) {
		ll mid = (left + right) / 2;
		if (money(mid)) right = mid;
		else left = mid;
	}

	cout << right << endl;

	return 0;
}