#include <stdio.h>

FILE *f,*g;
int zero(int n){
    int rasp=0;
    while (n>=5) {
        rasp+=n/5;
        n/=5;
    }
    /*while(x*5<=n){
        x*=5;
        rasp+=n/x;
    }*/
    return rasp;
}

int cautbin(int left, int right, int x){
    if(left==right){
        if(zero(right)==x)
            return right;
        else
            return -1;
    }
    int mid=(left+right)/2;
    if(zero(mid) >= x){
        return cautbin(left,mid,x);
    } else {
        return cautbin(mid+1,right,x);
    }
}

int main() {
    int p;
    f=fopen("fact.in","r");
    g=fopen("fact.out","w");
    fscanf(f,"%d",&p);
    fprintf(g,"%d",cautbin(1,100000000,p));
    return 0;
}