#include "bits/stdc++.h"
using namespace std;
#define fi first
#define se second
#define mp make_pair
#define pii pair<int,int>
#define yes cout<<"YES\n"
#define no cout<<"NO\n"
#define pb push_back
#define sz(x) (int)(x).size()
#define rsz resize
#define ass assign
#define F(i,l,r) for(int i=(l);i<(r);++i)
typedef long long ll;
typedef unsigned long long ull;
typedef long double lld;
template<typename T> using pqg = priority_queue<T, vector<T>, greater<T>>;
#define each(a,x) for(auto a:x)
#define FOR(i,a) for(int i=0;i<(a);i++)
#define ROF(i,a,b) for(int i=(b)-1;i>=(a);i--)
#define eb emplace_back
#define ft front()
#define V vector
void solve(){
ll r,u,n;
cin>>r>>u>>n;
if(n==1){
cout<<r<<'\n';
return;
}
if(n==2){
cout<<u<<'\n';
return;
}
ll v=1,vv=1;
F(i,3,n){
ll nxt=v+vv;
v=vv;
vv=nxt;
if(v>2e9 && vv>2e9)break;
}
ll a=v,b=vv,res=r*u;
if(r>b && u>a)res-=(r-b)*(u-a);
cout<<res<<'\n';
}
signed main(){
ios_base::sync_with_stdio(0);cin.tie(nullptr);
// #ifndef ONLINE_JUDGE
// freopen("output.txt", "w", stdout);
// freopen("input.txt", "r", stdin);
// freopen("Error.txt", "w", stderr);
// #endif
int tt=1;
//cin>>tt;
while(tt--)solve();
return 0;
}
