#include <stdio.h>
#include <math.h>
int main() {
    long long A, B, N, x, ans = 0;
    scanf("%lld %lld %lld", &A, &B, &N);
    x = B - 1 <= N ? B - 1 : N;
    ans = floor(A * x * 1.0 / B) - A * floor(x * 1.0 / B);
    printf("%lld\n", ans);
    return 0;
}