#include <stdio.h>
#include <stdlib.h>

int main(void){
    long long int a,b,n,max=0,before,after,x,f;
    (void)scanf("%lld %lld %lld",&a,&b,&n);
    for(x=0;x<=n;x++){
        before=(a*x)/b;
        after=x/b;
        f=before-a*after;
        if(f>max)max=f;
    }
    printf("%lld\n",max);
    return 0;
}