#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#include<stdbool.h>
#include<math.h>
#include<limits.h>

typedef long long ll;
ll A,B,N,ans;
int main(){
    scanf("%lld %lld %lld",&A,&B,&N);
    ll x = N-N%B-1;
    ll ans1 = (ll)((A*x)/B) - A*(ll)(x/B);
    ll ans2 = (ll)((A*N)/B) - A*(ll)(N/B);
    ll ans = ans1 > ans2 ? ans1 : ans2;
    printf("%lld",ans);
}
