#include <cstdio>
#include <iostream>
#include <cassert>
#include <string>
#include <algorithm>
#include <cstring>
#include <utility>
#include <vector>
#include <stack>
#include <queue>
#include <map>
#include <set>
#include <cmath>
#include <deque>
#include <unordered_map>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
#define IOS ios_base::sync_with_stdio(0); cin.tie(0)

using namespace std;
using namespace __gnu_pbds;
typedef long long LL;
typedef pair<int, int> pii;
typedef pair<LL, LL> pll;
typedef tree<int, null_type, less<int>, rb_tree_tag, tree_order_statistics_node_update> order_set;

int main() {
    LL A, B, N;
    scanf("%lld %lld %lld", &A, &B, &N);
    LL q1 = N / B, r1 = N % B;
    if (q1 == 0) printf("%lld\n", (r1 * A) / B);
    else printf("%lld\n", ((B - 1) * A) / B);
    return 0;
}
/* stuff you should look for
	* int overflow, array bounds
	* special cases (n=1?)
	* do smth instead of nothing and stay organized
	* WRITE STUFF DOWN
by Benq;
*/
