#include <stdio.h>
int zero(int x){
    int r=0;
    while(x>=5){
        r+=x/5;
        x/=5;
    }
    return r;
}

int caut(long long int p){
    int i=0,pas=1<<21;
    while(pas!=0){
        if(zero(i+pas)<p)
            i+=pas;
        pas/=2;
    }
    return 1+i;
}
int main(){
    FILE *fin,*fout;
    fin=fopen("fact.in","r");
    fout=fopen("fact.out","w");
    long long int p,rez;
    fscanf(fin,"%I64d",&p);
    rez=caut(p);
    if(zero(rez)!=p)
        rez=-1;
    fprintf(fout,"%I64d",rez);
    fclose(fin);
    fclose(fout);
    return 0;
}