#include<stdio.h>
#include<math.h>
int main(void){

    double a,b,n;

    scanf("%lf",&a);
    scanf("%lf",&b);
    scanf("%lf",&n);

    if(n < b){
        int d = (int) (a * n )/b;
        printf("%d",d);
    } else {
        int d = (int) (a * (b-1))/b;
        printf("%d",d);
    }

    return 0;

}