#include <stdio.h>
#include <math.h>

int main() {
    long long A, B, N;
    scanf("%lld %lld %lld", &A, &B, &N);
    int x[N+1], m = 0;

    for (int i = 0; i <= N; i++) {
        x[i] = floor(A * i / B) - A * floor(i / B);
        //printf("%d\n", x[i]);
    }
    for (int i = 0; i <= N; i++) {
        if (m < x[i]) {
            m = x[i];
        }
    }
    
    printf("%d\n", m);
    return 0;
}