#include <stdio.h>
#include <math.h>
int main() {
    long long A, B, N, max = 0;
    double x;
    scanf("%lld %lld %lld", &A, &B, &N);
    for (x = 0.0; x <= N; x += 1.0) {
        long long temp = floor(A * x / B) - A * floor(x / B);
        if (max < temp) max = temp;
    }
    printf("%lld\n", max);
    return 0;
}