#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <string.h>
#define MIN(x,y) ((x)<(y)?(x):(y))
#define MAX(x,y) ((x)<(y)?(y):(x))
#define MOD 1000000007LL
//#define MOD 998244353LL
//#define MOD 1000000009LL
const long long INF = 1LL << 60;
typedef long long ll;

int main(){
    ll A,B,N,temp;
    ll ans = 0;
    scanf("%lld %lld %lld",&A,&B,&N);
    temp = N-N%B-1;
    ans = temp*A/B-A*(temp/B);
    ans = (ans<N*A/B-A*(N/B)) ? N*A/B-A*(N/B) : ans;
    printf("%lld\n",ans);
    return 0;
}