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

int main(void){
    long long int a,b,n,max=0,before,after,x;
    (void)scanf("%lld %lld %lld",&a,&b,&n);
        x=b-1;
        if(n<x)x=n;
        before=(a*x)/b;
        after=x/b;
        max=before-a*after;
    printf("%lld\n",max);
    return 0;
}