#include<fstream>
using namespace std;

int cZ(int N){
    int c=0;
    while(N>=5){
        c+=N/5;
        N/=5;
    }
    return c;
}

int main(){
    ifstream fin("fact.in");
    ofstream fout("fact.out");
    int P;
    fin>>P;
    if(P==0){
        fout<<"1\n";
        return 0;
    }
    int left=0,right=P*5,ans=-1;
    while(left<=right){
        int mid=(left+right)/2;
        int zeroes=cZ(mid);
        if(zeroes==P){
            ans=mid;
            right=mid-1;
        }
        else if(zeroes<P){
            left=mid+1;
        }
        else{
            right=mid-1;
        }
    }
    fout<<ans<<"\n";
    return 0;
}