#include <stdio.h>
#include<stdlib.h>
#include<string.h>
#include <assert.h>

int main(void){
		long long int a,b,c;
    long long int ans;
		scanf("%lld",&a);
    scanf("%lld",&b);
    scanf("%lld",&c);
    int x = 0;

    if(c<b){
      x = c;
    }
    else{
      x = b-1;
    }




    ans = (a*x/b) - a*(x/b);


    printf("%lld\n",ans);


		return 0;
}
