#include <stdio.h>

int main(void)
{
    int a,b,n;
    scanf("%d %d %d",&a,&b,&n);

    int ans=-10000000;

    for(int i=0;i<n+1;i++){
        int x=a*i/b;
        int y=i/b;
        y*=a;
        if(x-y>ans){
            ans=x-y;
        }
    }
    printf("%d",ans);
    return 0;
}