#include <stdio.h>
int zero(int n){
    int r=0;
    while(n>=5){
        r+=n/5;
        n/=5;
    }
    return r;
}
int cout(int p){
    int i=0,pas=1<<29;
    while(pas!=0){
        if(zero(i+pas)<p)
            i+=pas;
        pas/=2;
    }
    return i+1;
}
int main(){
    int p,r;
    FILE *fin,*fout;
    fin=fopen("fact.in","r");
    fout=fopen("fact.out","w");
    fscanf(fin,"%d",&p);
    r=cout(p);
    if(zero(r)==p)
        fprintf(fout,"%d",r);
    else fprintf(fout,"-1");
    return 0;
}