#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <math.h>
#define ull unsigned long long

int main(){
    double alpha = 0.0;
    ull a,b,n,x,k,max=0;
    scanf("%lld%lld%lld",&a,&b,&n);
    for (x=n-(ull)pow(n, 0.69); x<=n; x++) {
        k=x/b;alpha=(double)x/b-(double)k;
        if (max<=(ull)(a*alpha)) max=(ull)(a*alpha);
    }
    printf("%lld",max);
    return 0;
}
