#include <stdio.h>
int main(void){
    int a;
    long b,n;
    scanf("%d %ld %ld",&a,&b,&n);
    if(a==1)
        printf("0");
    else if(n<b)
        printf("%ld",(a*n)/b-a*(n/b));
    else
        printf("%ld",(a*(b-1))/b-a*((b-1)/b));
}
