#include <iostream.h>
#include <math.h>

int main(void)
{
    int K;
    int ind = 1;
    int L = 0;

    cin >> K;

    if( !(K % 2) )
    {
        while( (!(K % 2)) && (K > 4) )
            K /= 2;

        L = K - 1;
        ind = 0;
    };

    for(int i = 3 ; ( i <= ceil( sqrt(K) ) ) && ind ; ++i)
    {
        if( !(K % i) )
        {
            L = i - 1;
            ind = 0;
        };
    };

    if( (K != 1) && (L == 0) )
        L = K - 1;
    cout << L;

    return 0;
};
//I compiled it under bc 3.0, vc 7.0, vc 6.0
//Please HELP

   My program got CE at the first,but when I changed sqrt(K) to
sqrt((double)K),it got AC.Maybe you can have a try,good luck&#1032;&#1038;