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

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

    int x;
    for(x=n;1;x--){
        tmp=floorl(a*x/b)-a*floorl(x/b);
        if(tmp<max){
            break;
        }
        if(tmp>=max){
            max=tmp;
        }
    }
    printf("%ld\n",(long)max);

    return 0;
}
