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

int main()
{
    long long int a,b,n;

    scanf("%lld %lld %lld",&a,&b,&n);

    long long int ans;

    if(b-1 > n)
        ans = (a*n)/b;
    else
        ans = (a*(b-1))/b;

    printf("%lld\n",ans);

    return 0;
}