#include<stdio.h>

int main() {
	int a, b, n, m,ma,mb,ans;
	scanf("%d %d %d", &a, &b, &n);
	ma = (a*0) / b;
	mb = a*(0 / b);
	ans = ma - mb;
	for (int i = 1; i <= n; i++) {
		ma = (a*i) / b;
		mb = a*(i / b);
		m = ma - mb;
		if (m > ans) {
			ans = m;
		}
	}
	printf("%d", ans);
}