#include <stdio.h>

int nr0(int n){
    int p=1,cif5=0;
    p=1;
    while(p*5<=n){
        p=p*5;
        cif5=cif5+n/p;
    }
    return cif5;
}

int main()
{
    FILE *fin,*fout;
    fin=fopen("factorial.in","r");
    fout=fopen("factorial.out","w");
    int p,st,dr,mij,poz=-1,pf;
    fscanf(fin,"%d",&p);
    if(p==0){
        fprintf(fout,"1");
    }
    else{
        st=1;
        dr=p*10;
        while(st<=dr){
            mij=(dr+st)/2;
            pf=nr0(mij);
            if(pf<p)
                st=mij+1;
            if(pf>p)
                dr=mij-1;
            if(pf==p){
                poz=mij;
                dr=mij-1;
            }
        }
        fprintf(fout,"%d",poz);
    }
    return 0;
}