#include<stdio.h>
#define ll long long
ll llgcd(ll a, ll b){return b == 0 ? a : llgcd(b, a % b);}
ll lllcm(ll a, ll b){return a / llgcd(a, b) * b;}
int main(){
    long long a, b, n, ans = 0;
    scanf("%lld%lld%lld",&a,&b,&n);
    if(n < b)
        ans = n;
    else 
        ans = b - 1;
    ans *= a;
    ans /= b;
    printf("%lld\n",ans);
    return 0;
}