#include"bits/stdc++.h"

//#include<bits/stdc++.h>
using namespace std;
#define print(x) cout<<x<<endl;
#define rep(i,a,b) for(int i=a;i<b;i++)
#define REP(i,a) for(int i=0;i<a;i++)
typedef long long ll;
typedef pair<int, int> PI;
typedef pair<int, PI> V;
typedef vector<int> VE;
const ll mod = 1000000000;

int main() {
	double a, b, t;
	cin >> a >> b >> t;
	ll n = ceil(t / b);
	double min_ = mod;
	REP(i, n+1) {
		ll m = max(0.0,ceil((t - b*i) / a));
		min_ = min(min_, b*i+a*m);
	}
	print(min_);
	return 0;
}