C :

#include<stdio.h>
int main()
{
    double h,a,b,n,s;
    while(scanf("%lf%lf%lf",&h,&a,&b)!=EOF)
    if(h>a&&a<=b) printf("-1\n");
    else
    {
        for(n=1;; n++)
        {
            s=a*n-(n-1)*b;
            if(s>=h) break;
        }
        printf("%.lf\n",n);
    }
    return 0;
}

C++ :

#include<iostream>
#include<cstdio>
#include<string>
#include<cstring>
#include<cmath>
#include<algorithm>
#include <fstream>
#include <limits>
#include <vector>
#include <list>
#include <set>
#include <map>
#include <queue>
#include <stack>
#include <cassert>
using namespace std;
int main()
{
    int i;
    double h,a,b;
    while(~scanf("%lf %lf %lf",&h,&a,&b))
    {
        if(a<=b)
        {
            if(h<=a)
                printf("1\n");
            else
                printf("-1\n");
        }
        else
        {
            double da=((h-a)/(a-b)+1);
            if(fabs(da-(int)da)>=1e-5)
                da++;
            printf("%d\n",(int)da);
        }
    }
return 0;
}