#include <fstream>

using namespace std;

ifstream cin("fact.in");
ofstream cout("fact.out");

long long m5fact(long long n){
    unsigned long long sum=0,m5=5;
    while(n/m5!=0){
        sum+=n/m5;
        m5*=5;
    }
    return sum;
}

long long cautb(long long n){
    long long pas=1<<23,r=0;
    while(pas!=0){
        if(m5fact(r+pas)<n){
            r+=pas;
        }
        pas/=2;
    }
    return r+1;
}

int main()
{
    long long p;
    cin>>p;
    cout<<cautb(p);
    return 0;
}