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

    int a,b,n;

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

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

    return 0;



}