include <bits/stdc++.h>

define ll long long

using namespace std;
ll a,b,k;
int main()
{
cin >> a >> b >> k;
ll bop = min(a,b);
ll c = k;
c = k *(k+1) / 2;
if (c <= bop)
{
a -= c;
b -= c;
cout << a + b;
return 0;
}
cout << max(a,b) - bop;
}