#include <fstream>

using namespace std;
ifstream fcin("fact.in");
ofstream fout("fact.out");
long long p,st,dr,sol;
long long legendre(long long val)
{
    long long s=0;
    long long power=5;
    while(val/power>0 && power<(1<<30))
    {
        s=s+val/power;
        power=power*5;
    }
    return s;
}
int main()
{
    fcin>>p;
    st=1;
    dr=500000000;
    while(st<=dr)
    {
        long long mij=(st+dr)/2;
        if(legendre(mij)>=p)
        {
            sol=mij;
            dr=mij-1;
        }
        else
        {
            st=mij+1;
        }
    }
    fout<<sol;
    return 0;
}