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