#include<stdio.h>

int main(){
    long long int a,b,n,res = 0,resold = 0,i;

    scanf("%lld %lld %lld",&a,&b,&n);

    for( i = 1; i <= n ; i++ ){
        resold = res;
        res = ( ( a * i ) / b ) - a * ( i / b );
        if( resold > res ){
            res = resold;
            break;
        }
    }

    printf("%lld\n",res);
}