#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <math.h>
int main(void){
    long int a,b,n,i,owari;
    long int ans=0;
    scanf("%ld %ld %ld",&a,&b,&n);
    if(b>n)owari=n;
    else owari=b-1;
    ans = floor(a*owari/b) - a*floor(owari/b);
    printf("%ld",ans);
    return 0;
}