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

#define max  100000

//qsort(str, n, sizeof(int), up_comp);
int up_comp(const void *a, const void *b){return *(int*)a - *(int*)b;}
int down_comp(const void *a, const void *b){return *(int*)b - *(int*)a;}
int count_digit(int a){int i=0;while(a!=0){a=a/10;i++;}return i;}
int euclid( int a, int b ){int temp;if(a<b){temp=a;a=b;b=temp;}if(b<1)return -1;if(a%b==0) return b;return euclid(b,a%b);}
int int_sort( const void * a , const void * b ) {
  return strcmp(( char * )a , ( char * )b );
}

int main()
{
    int  f1, f2, ans, tmp=0;
    long int a, b, x, n;
    
    scanf("%ld%ld%ld", &a, &b, &n);
    
    for (x=0; x<=n; x++) {
        f1=floor((double)a*x/b);
        f2=a*floor((double)x/b);
        ans=f1-f2;
        if (ans>tmp) {
            tmp=ans;
        }
    }
    
    printf("%d", tmp);
    
    return 0;
} 

