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

int main(void){

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

    long a[B];
    for (long x = 0; x < B; x++){
        a[x] = floor((double)(A * (x + 1)) / B) - A * floor((double)(x + 1) / B);
    }

    while (i < N){
        if (Max < a[i]){
            Max = a[i];
        }
        if (i > N){
            break;
        }
        i++;
    }
    printf("%ld\n", Max);

    return 0;
}