#include<fstream>
#include<math.h>
using namespace std;
int caut_fact(int z)
{
    long long i,s=0,st=1,dr=5*(1e8),y=1;
    while(st<=dr)
    {
    int mid=(st+dr)/2;
    while(y<=mid)
    {
        y=y*5;
        s=s+mid/y;
    }
    if(z<=s)
    {
        dr=mid-1;
    }
    else
    {
        st=mid+1;
    }
    s=0;
    y=1;
    }

    return st;
}
int main()
{
    ifstream fin ("fact.in");
    ofstream fout ("fact.out");
    unsigned long long x;
    fin>>x;
    fout<<caut_fact(x);
}