#include<stdio.h>
int p;
int zero ( int n){
    int rez=0;
    while(n>=5){
        rez+=n/5;
        n/=5;
    }
    return rez;
}
int caut ( int numar){
    int i=1, pas=1<<23;
    while(pas!=0){
        if(zero(i+pas)<p)
            i+=pas;
        pas>>=1;
    }
    if(zero(i+1+pas)==p)
        return i+1;
    return -1;
}
int main(){
    int x;
    freopen("fact.in","r",stdin);
    freopen("fact.out","w",stdout);
    scanf("%d",&p);
    if(p==0)
        printf("1\n");
    else{
        x=caut(p);
        printf("%d\n",x);
    }
    return 0;
}