wrong code

XDU 1060

#include <cstdio>
#include <iostream>
#include <stack>

using namespace std;

stack<int> m1;
stack<int> m2;
int main()
{
string s;
while(cin >> s)
{
int len  = s.size(), i;
if(len == 1)
{
cout << "0.0";
int r = s[0] - '0';
r = r >= 5? 1: 0;
cout << r << endl;
}
else if(len == 2)
{
cout << "0.";
for(i = 0; i < len-1; i++)
{
m1.push(s[i]-'0');
}
int r = s[i] - '0';
r >= 5? r = 1: r = 0;
while(!m1.empty())
{
r += m1.top();
m2.push(r%10);
m1.pop();
r /= 10;
}
if(r)
m2.push(r);
if(m2.size() == 2)
{
cout << m2.top();   m2.pop();
cout << m2.top();   m2.pop();
}
else
{
cout << 0 << m2.top();
m2.pop();
}
cout << endl;
}
else if(len == 3)
{
cout << "0.";
for(i = 0; i < len-1; i++)
{
m1.push(s[i]-'0');
}
int r = s[i] - '0';
r >= 5? r = 1: r = 0;
while(!m1.empty())
{
r += m1.top();
m2.push(r%10);
m1.pop();
r /= 10;
}
if(r)
m2.push(r);
cout << m2.top();   m2.pop();
cout << m2.top();   m2.pop();
cout << endl;
}
else
{
for(i = 0; i < len-1; i++)
{
m1.push(s[i]-'0');
}
int r = s[i] - '0';
r >= 5? r = 1: r = 0;
while(!m1.empty())
{
r += m1.top();
m2.push(r%10);
m1.pop();
r /= 10;
}
if(r)
m2.push(r);
int m_len = m2.size();
for(int i = 1; i <= m_len-2; i++)
{
cout << m2.top();
m2.pop();
}
cout << '.';
while(!m2.empty())
{
cout << m2.top();
m2.pop();
}
cout << endl;
}

}

}