#include <fstream>
#include <cmath>
using namespace std;
ifstream in("fact.in");
ofstream out("fact.out");
int p,st=1,dr=100000000*5+5,mij,x,zerouri,i;
int power(int x)
{
    int rez=1;
    for (int i=1;i<=x;++i)
        rez*=5;
    return rez;
}
int main()
{
    in>>p;
    while (st<dr)
    {
        mij=(st+dr)/2;
        zerouri=0;
        x=log2(mij*1.0)/log2(5.0);
        for (i=1;i<=x;++i) zerouri+=mij/power(i);
        if (zerouri<p) st=mij+1;
        else dr=mij;
    }
    out<<dr;
}