#include <iostream>
#include <fstream>
#define int long long
using namespace std;

int beibi(int x)
{
    int cnt=0;
    while(x>0)
    {
        cnt+=x/5;
        x=x/5;
    }
    return cnt;
}
signed main()
{
    ifstream cin ("fact.in");
    ofstream cout("fact.out");
    
    int n, st=0, dr=100000000000000, mid;
    cin>>n;
    while(dr-st>1)
    {
        mid=(st+dr)/2;
        if(beibi(mid)<n)
        st=mid;
        else
        dr=mid;
    }
    cout<<dr;

    return 0;
}