#include <fstream>

using namespace std;

ifstream fin("fact.in");
ofstream fout("fact.out");

long long Zerouri(long long a)
{
    long long z = 0;
    for( long long  i = 5; i <= a; i *= 5 )
        z += a / i;
    return z;
}

int main()
{
    long long Infi = 1 << 30, p;
    fin >> p;
    long long step = Infi, ans;
    for(ans = 0; step; step >>= 1 )
        if( ans + step <= Infi && Zerouri(ans + step) <= p )
            ans += step;
    if( !ans )
        fout << -1;
    else
    {
        while( ans % 5 != 0 )
            ans--;
        fout << ans;
    }
    return 0;
}