#include<stdio.h>
int main(void){
    long int A, B, N,  X, Y, ch, count=0,ans=0;
        scanf("%ld%ld%ld",&A,&B,&N);
    for(int x=1;x<=N;x++){
        X=(A*x)/B;
        Y=(x/B);
        //printf("x=%dの時、[(A*x)/B]:%d, [x/B]:%d\n", x, (A*x)/B, x/B);
       ch= ( X -A*Y );
       if(ch > count){
           count=ch;
       }
    }
printf("%d\n",count);
return 0;
}