#include <iostream>
#include <fstream>
using namespace std;

int main()
{
    long long int P,N,contor=0,i,st,dr,mid,ans;
    ifstream fin("fact.in");
    ofstream fout("fact.out");
    st=1;
    dr=5e8;
    fin>>P;
    while(st<=dr)
    {
        mid=(st+dr)/2;
        contor=0;
        for(i=5;i<=mid;i*=5)
        {
            contor=contor+mid/i;
        }
        if(contor>=P)
        {
            ans=mid;
            dr=mid-1;
        }
        else
        {
            st=mid+1;
        }
    }
    fout<<ans;
    return 0;
}