#include <stdio.h>
int main(void){
   long long int a, b, n;
   scanf("%lld%lld%lld", &a, &b, &n);
    long long int x;
    x = b / a;
    if(x == 0){
        x = 1;
    }
    long long int ans, d, e;
    d = a * n / b;
    e = n / b;
    ans = d - a * e;
    for(long long int i = n - 1; x <= i; i--){
        long long int  c, f, g;
        f = a * i / b;
        g = i / b;
        c = f - a * g;
        if(ans < c){
            ans = c;
        }else{
            printf("%lld", ans);
            return 0;
        }
    }

    
}