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

int main(void){
    long double a,b,n,tmp,max=0;
    scanf("%Lf %Lf %Lf",&a,&b,&n);

    int x;
    for(x=0;x<=n;x++){
        tmp=floorl(a*x/b)-a*floorl(x/b);
        if(tmp>max){
            max=tmp;
        }
    }
    printf("%ld\n",(long)max);

    return 0;
}
