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

int main(void){

    long A = 0;
    long B = 0;
    long N = 0;
    long i = 0;
    long long max = 0;
    long long tmp = 0;
    scanf("%ld %ld %ld", &A, &B, &N);

    for (long x = 0; x < B; x++){
        tmp = (A * (x + 1)) / B - A * ((x + 1) / B);

        if (max < tmp && x < N){
            max = tmp;
        }
        if (x == N){
            break;
        }
    }
    printf("%lld\n", max);

    return 0;
}