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

