cf Perfect Pair

http://codeforces.com/contest/318/problem/C

#include <cstdio>
#include <cstring>
#include <algorithm>
using namespace std;
long long j;
long long x,y,m;
int main()
{
    scanf("%I64d%I64d%I64d",&x,&y,&m);
    if(x>=m||y>=m)
    {
        printf("0
");
        return 0;
    }
    else if(x<=0&&y<=0)
    {
        printf("-1
");
        return 0;
    }
    if(x<0)
    {
        j=(-x)/y+1;
        x+=j*y;
    }
    if(y<0)
    {
        j=(-y)/x+1;
        y+=j*x;
    }
    while(1)
    {
        if(!(x<m&&y<m)) break;
        if(x>y) y=x+y;
        else x=x+y;
        j++;
    }
    printf("%I64d
",j);
    return 0;
}