#include <bits/stdc++.h>

using namespace std;

struct UnionFind
{
  vector< int > data;

  UnionFind(int sz)
  {
    data.assign(sz, -1);
  }

  bool unite(int x, int y)
  {
    x = find(x), y = find(y);
    if(x == y) return (false);
    if(data[x] > data[y]) swap(x, y);
    data[x] += data[y];
    data[y] = x;
    return (true);
  }

  int find(int k)
  {
    if(data[k] < 0) return (k);
    return (data[k] = find(data[k]));
  }

  int size(int k)
  {
    return (-data[find(k)]);
  }
};

typedef long long int64;

void solve()
{
  int64 a, b, c;
  cin >> a >> b >> c;
  cout << ((b - c) * c - (b * b - a * c)) / (a - b) << endl;
}

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