// 区间中点覆盖长度最大贪心
// 1452E - Two Editorials
#include<bits/stdc++.h>
using namespace std;
const int N = 2005;
int n, m, k, ans;
int suffix[N];
struct Interval
{
    int l, r;
    bool operator< (const Interval &Other) const {
         return l + r < Other.l + Other.r; // 区间中点排序（处理重合）intersec相交
    }
}Intervals[N];

int main(){
    cin >> n >> m >> k;
    for(int i = 0; i < m; i ++ ){
        int l, r;
        scanf("%d%d", &l, &r);
        Intervals[i] = {l - 1, r}; // 左端点--这样右端点减去左端点就是长度
    }
    sort(Intervals, Intervals + m);
    for(int i = 0; i + k <= n; i ++ ){
        int sum = 0;
        for(int j = m - 1; j >= 0; j -- ){
            sum  += max(0, min(i + k, Intervals[j].r) - max(i, Intervals[j].l));
            suffix[j] = max(suffix[j], sum);
        }
    }
    for(int i = 0; i + k <= n; i ++ ){
        int sum = 0;
        for(int j = 0; j <= m - 1; j ++ ){
            sum  += max(0, min(i + k, Intervals[j].r) - max(i, Intervals[j].l));
            ans = max(ans, suffix[j + 1] + sum);
        }
    }
    cout << ans;
    return 0;
}