CodeForces 34C Page Numbers

#include <iostream>
#include <cstdlib>
#include <cstring>
#include <string>
#include <cstdio>
#include <cmath>
#include <algorithm>
#include <vector>
#include <queue>
#include <map>
#define inf 0x3f3f3f3f
#pragma comment(linker, "/STACK:16777216")
#define eps 1e-6
#define ll long long
using namespace std;
inline int ReadInt()
{
    char ch = getchar();
    if (ch==EOF) return -1;
    int data = 0;
    while (ch < '0' || ch > '9')
    {
        ch = getchar();
        if (ch==EOF) return -1;
    }
    do
    {
        data = data*10 + ch-'0';
        ch = getchar();
    } while (ch >= '0' && ch <= '9');
    return data;
}
int s[110];
int main()
{
    int i=0,n;
    while((s[i]=ReadInt())!=-1) i++;
    n=i;
    sort(s,s+n);
    printf("%d",s[0]);
    int flag=0;
    for(i=1;i<n;i++)
    {
        if(s[i]==s[i-1]) continue;
        if(s[i]-s[i-1]==1)
        {
            if(flag) continue;
            else
            {
                flag=1;
                printf("-");
                continue;
            }
        }
        if(flag==1)
        {
            flag=0;
            printf("%d",s[i-1]);
        }
        printf(",%d",s[i]);
    }
    if(flag==1)
    {
        flag=0;
        printf("%d",s[i-1]);
    }
    puts("");
    return 0;
}