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


int main() {
  long long a, b, n;
  scanf("%lld %lld %lld", &a, &b, &n);

//  for(long long i=0;i<=n;i++){
//    long long val = floor((double)a*(double)i/(double)b) - a*floor((double)i/(double)b);
//    printf("x=%lld | %lld\n", i, val);
//  }
  long long val;
  if(n>b-1){
    val = floor((double)a*(double)(b-1)/(double)b) - a*floor((double)(b-1)/(double)b);
  }
  else{
    val = floor((double)a*(double)(n)/(double)b) - a*floor((double)(n)/(double)b);
  }
  printf("%lld", val);
  return 0;
} 