#include <stdio.h>

int main()
{

    long a,b,n;
    
    scanf("%ld %ld %ld", &a, &b,&n);

    long x;
    x = 1;
    x = b - 1;
    if(n<x)
        x = n;

    long fb = x / b;
    long fa = (a * x) / b;
    long ans = fa - a * fb;

    printf("%ld",ans);
    

    printf("\n");
}