#include <fstream>

using namespace std;

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

int fact(int n){
    int ctr=0;
    while(n>=5){
        ctr+=n/5;
        n/=5;
    }
    return ctr;
}

int main()
{
    int p;
    cin>>p;

    int st=1, dr=1e9, rez = dr+1;

    while(st<=dr){
        int m= (st+dr)/2;
        if(fact(m)>=p){
            dr=m-1;
            rez=m;
        }
        else{
            st=m+1;
        }
    }
    cout<<rez;
    return 0;
}