//#include<bits/stdc++.h>
#include<iostream>
#include<math.h>
#include<cstring>
#include<string.h>
#include<algorithm>
#include<stdio.h>
using namespace std;

int main()
{
	long long x,y,n,ans;
	cin>>x>>y>>n;
	x--;
	y--;
	
	for(;n>=10;n-=10,ans+=y);
	cout<<ans+n*x;
	return 0;
}