#include<fstream>
#include<climits>
#define int long long
using namespace std;
ifstream fin("fact.in");
ofstream fout("fact.out");

int Nr_0_final(int n){

int s=0,i,c=5;

while(n >= c){
    s+=n/c;
    c*=5;
}

return s;

}

int32_t main(){

int st,dr,mij,rez=-1,p,n,x;

fin>>p;

st=0;
dr =400000015;

while(st<=dr){

    mij=(st+dr)/2;

    x = Nr_0_final(mij);

    if(x == p)
        rez=mij;

    if(x >= p)
        dr=mij-1;
    else
        st=mij+1;

}


fout<<rez;
}