#include <stdio.h>

int main(void){
    long int a,b,n,lp,lq;
    long int max = 0;
    int maxNum;
    scanf("%ld%ld%ld",&a,&b,&n);
    if(0 < n < 100){
        for(long int i =0; i <=n; i++){
            lp = a*i/b;
            lq = i/b;
            long int ans = lp - a * lq;
            if(max < ans){
                max = ans;
            }
        }
    }else{
        long int data[20];
        data[0] = n/20;
        for(int i = 1; i < 10;i++){
            data[i] = data[i-1] + n/10;
        }
        for(int i = 0; i < 20;i++){
            lp = a*data[i]/b;
            lq = data[i]/b;
            long int ans = lp - a * lq;
            if(max < ans){
                maxNum = i;
                max = ans;
            }
        }
        for (int i = data[maxNum-1];i < data[maxNum + 1];i++){
            lp = a*i/b;
            lq = i/b;
            long int ans = lp - a * lq;
            if(max < ans){
                maxNum = i;
            }
        }
    }
    printf("%d",max);
    return 0;
}