#include <stdio.h>
#include <stdlib.h>
#include <math.h>

typedef long long ll;

int main(void)
{
    ll a,b,n,x;
    ll ans;
    scanf("%llu %llu %llu", &a,&b,&n);
    ll big = 0;
    for(x = 1; x <= n; x++)
    {
        ans = floor((a*x)/b)- a*(floor(x/b));
        if(ans > big)
            big = ans;
    }
    printf("%llu\n", big);
}
