#include <stdio.h>

void main(void){
    long a,b,n,x,res,res1,res2, max=0;

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

    for(x=0;x<=n;x++){
        res1 = a*x/b;
        res2 = x/b;
        if(res2<1)
            res = res1;
        else
            res= res1-a*res2;
        if(res<0)
            break;
        if(res>max){
            max=res;
        }
    }
    printf("%ld\n", max);
}