#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <math.h>
#define ll long long int

int main(void)
{

    ll a, b, n;
    ll max = 0;
    ll ans, i, ch;
    scanf("%lld %lld %lld", &a, &b, &n);
    if (b < n)
    {
        max = (a * (b - 1)) / b;
    }
    else
    {
        max = (a * n) / b;
    }
    printf("%lld\n", max);

    return 0;
}